File: config.sgml

package info (click to toggle)
postgresql-9.6 9.6.15-0+deb9u1
  • links: PTS, VCS
  • area: main
  • in suites: stretch
  • size: 129,420 kB
  • sloc: ansic: 742,939; sql: 67,276; xml: 30,901; yacc: 30,445; perl: 16,293; lex: 7,764; sh: 5,290; makefile: 4,780; python: 112; asm: 65; sed: 15
file content (8325 lines) | stat: -rw-r--r-- 353,632 bytes parent folder | download
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
2080
2081
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104
2105
2106
2107
2108
2109
2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
2121
2122
2123
2124
2125
2126
2127
2128
2129
2130
2131
2132
2133
2134
2135
2136
2137
2138
2139
2140
2141
2142
2143
2144
2145
2146
2147
2148
2149
2150
2151
2152
2153
2154
2155
2156
2157
2158
2159
2160
2161
2162
2163
2164
2165
2166
2167
2168
2169
2170
2171
2172
2173
2174
2175
2176
2177
2178
2179
2180
2181
2182
2183
2184
2185
2186
2187
2188
2189
2190
2191
2192
2193
2194
2195
2196
2197
2198
2199
2200
2201
2202
2203
2204
2205
2206
2207
2208
2209
2210
2211
2212
2213
2214
2215
2216
2217
2218
2219
2220
2221
2222
2223
2224
2225
2226
2227
2228
2229
2230
2231
2232
2233
2234
2235
2236
2237
2238
2239
2240
2241
2242
2243
2244
2245
2246
2247
2248
2249
2250
2251
2252
2253
2254
2255
2256
2257
2258
2259
2260
2261
2262
2263
2264
2265
2266
2267
2268
2269
2270
2271
2272
2273
2274
2275
2276
2277
2278
2279
2280
2281
2282
2283
2284
2285
2286
2287
2288
2289
2290
2291
2292
2293
2294
2295
2296
2297
2298
2299
2300
2301
2302
2303
2304
2305
2306
2307
2308
2309
2310
2311
2312
2313
2314
2315
2316
2317
2318
2319
2320
2321
2322
2323
2324
2325
2326
2327
2328
2329
2330
2331
2332
2333
2334
2335
2336
2337
2338
2339
2340
2341
2342
2343
2344
2345
2346
2347
2348
2349
2350
2351
2352
2353
2354
2355
2356
2357
2358
2359
2360
2361
2362
2363
2364
2365
2366
2367
2368
2369
2370
2371
2372
2373
2374
2375
2376
2377
2378
2379
2380
2381
2382
2383
2384
2385
2386
2387
2388
2389
2390
2391
2392
2393
2394
2395
2396
2397
2398
2399
2400
2401
2402
2403
2404
2405
2406
2407
2408
2409
2410
2411
2412
2413
2414
2415
2416
2417
2418
2419
2420
2421
2422
2423
2424
2425
2426
2427
2428
2429
2430
2431
2432
2433
2434
2435
2436
2437
2438
2439
2440
2441
2442
2443
2444
2445
2446
2447
2448
2449
2450
2451
2452
2453
2454
2455
2456
2457
2458
2459
2460
2461
2462
2463
2464
2465
2466
2467
2468
2469
2470
2471
2472
2473
2474
2475
2476
2477
2478
2479
2480
2481
2482
2483
2484
2485
2486
2487
2488
2489
2490
2491
2492
2493
2494
2495
2496
2497
2498
2499
2500
2501
2502
2503
2504
2505
2506
2507
2508
2509
2510
2511
2512
2513
2514
2515
2516
2517
2518
2519
2520
2521
2522
2523
2524
2525
2526
2527
2528
2529
2530
2531
2532
2533
2534
2535
2536
2537
2538
2539
2540
2541
2542
2543
2544
2545
2546
2547
2548
2549
2550
2551
2552
2553
2554
2555
2556
2557
2558
2559
2560
2561
2562
2563
2564
2565
2566
2567
2568
2569
2570
2571
2572
2573
2574
2575
2576
2577
2578
2579
2580
2581
2582
2583
2584
2585
2586
2587
2588
2589
2590
2591
2592
2593
2594
2595
2596
2597
2598
2599
2600
2601
2602
2603
2604
2605
2606
2607
2608
2609
2610
2611
2612
2613
2614
2615
2616
2617
2618
2619
2620
2621
2622
2623
2624
2625
2626
2627
2628
2629
2630
2631
2632
2633
2634
2635
2636
2637
2638
2639
2640
2641
2642
2643
2644
2645
2646
2647
2648
2649
2650
2651
2652
2653
2654
2655
2656
2657
2658
2659
2660
2661
2662
2663
2664
2665
2666
2667
2668
2669
2670
2671
2672
2673
2674
2675
2676
2677
2678
2679
2680
2681
2682
2683
2684
2685
2686
2687
2688
2689
2690
2691
2692
2693
2694
2695
2696
2697
2698
2699
2700
2701
2702
2703
2704
2705
2706
2707
2708
2709
2710
2711
2712
2713
2714
2715
2716
2717
2718
2719
2720
2721
2722
2723
2724
2725
2726
2727
2728
2729
2730
2731
2732
2733
2734
2735
2736
2737
2738
2739
2740
2741
2742
2743
2744
2745
2746
2747
2748
2749
2750
2751
2752
2753
2754
2755
2756
2757
2758
2759
2760
2761
2762
2763
2764
2765
2766
2767
2768
2769
2770
2771
2772
2773
2774
2775
2776
2777
2778
2779
2780
2781
2782
2783
2784
2785
2786
2787
2788
2789
2790
2791
2792
2793
2794
2795
2796
2797
2798
2799
2800
2801
2802
2803
2804
2805
2806
2807
2808
2809
2810
2811
2812
2813
2814
2815
2816
2817
2818
2819
2820
2821
2822
2823
2824
2825
2826
2827
2828
2829
2830
2831
2832
2833
2834
2835
2836
2837
2838
2839
2840
2841
2842
2843
2844
2845
2846
2847
2848
2849
2850
2851
2852
2853
2854
2855
2856
2857
2858
2859
2860
2861
2862
2863
2864
2865
2866
2867
2868
2869
2870
2871
2872
2873
2874
2875
2876
2877
2878
2879
2880
2881
2882
2883
2884
2885
2886
2887
2888
2889
2890
2891
2892
2893
2894
2895
2896
2897
2898
2899
2900
2901
2902
2903
2904
2905
2906
2907
2908
2909
2910
2911
2912
2913
2914
2915
2916
2917
2918
2919
2920
2921
2922
2923
2924
2925
2926
2927
2928
2929
2930
2931
2932
2933
2934
2935
2936
2937
2938
2939
2940
2941
2942
2943
2944
2945
2946
2947
2948
2949
2950
2951
2952
2953
2954
2955
2956
2957
2958
2959
2960
2961
2962
2963
2964
2965
2966
2967
2968
2969
2970
2971
2972
2973
2974
2975
2976
2977
2978
2979
2980
2981
2982
2983
2984
2985
2986
2987
2988
2989
2990
2991
2992
2993
2994
2995
2996
2997
2998
2999
3000
3001
3002
3003
3004
3005
3006
3007
3008
3009
3010
3011
3012
3013
3014
3015
3016
3017
3018
3019
3020
3021
3022
3023
3024
3025
3026
3027
3028
3029
3030
3031
3032
3033
3034
3035
3036
3037
3038
3039
3040
3041
3042
3043
3044
3045
3046
3047
3048
3049
3050
3051
3052
3053
3054
3055
3056
3057
3058
3059
3060
3061
3062
3063
3064
3065
3066
3067
3068
3069
3070
3071
3072
3073
3074
3075
3076
3077
3078
3079
3080
3081
3082
3083
3084
3085
3086
3087
3088
3089
3090
3091
3092
3093
3094
3095
3096
3097
3098
3099
3100
3101
3102
3103
3104
3105
3106
3107
3108
3109
3110
3111
3112
3113
3114
3115
3116
3117
3118
3119
3120
3121
3122
3123
3124
3125
3126
3127
3128
3129
3130
3131
3132
3133
3134
3135
3136
3137
3138
3139
3140
3141
3142
3143
3144
3145
3146
3147
3148
3149
3150
3151
3152
3153
3154
3155
3156
3157
3158
3159
3160
3161
3162
3163
3164
3165
3166
3167
3168
3169
3170
3171
3172
3173
3174
3175
3176
3177
3178
3179
3180
3181
3182
3183
3184
3185
3186
3187
3188
3189
3190
3191
3192
3193
3194
3195
3196
3197
3198
3199
3200
3201
3202
3203
3204
3205
3206
3207
3208
3209
3210
3211
3212
3213
3214
3215
3216
3217
3218
3219
3220
3221
3222
3223
3224
3225
3226
3227
3228
3229
3230
3231
3232
3233
3234
3235
3236
3237
3238
3239
3240
3241
3242
3243
3244
3245
3246
3247
3248
3249
3250
3251
3252
3253
3254
3255
3256
3257
3258
3259
3260
3261
3262
3263
3264
3265
3266
3267
3268
3269
3270
3271
3272
3273
3274
3275
3276
3277
3278
3279
3280
3281
3282
3283
3284
3285
3286
3287
3288
3289
3290
3291
3292
3293
3294
3295
3296
3297
3298
3299
3300
3301
3302
3303
3304
3305
3306
3307
3308
3309
3310
3311
3312
3313
3314
3315
3316
3317
3318
3319
3320
3321
3322
3323
3324
3325
3326
3327
3328
3329
3330
3331
3332
3333
3334
3335
3336
3337
3338
3339
3340
3341
3342
3343
3344
3345
3346
3347
3348
3349
3350
3351
3352
3353
3354
3355
3356
3357
3358
3359
3360
3361
3362
3363
3364
3365
3366
3367
3368
3369
3370
3371
3372
3373
3374
3375
3376
3377
3378
3379
3380
3381
3382
3383
3384
3385
3386
3387
3388
3389
3390
3391
3392
3393
3394
3395
3396
3397
3398
3399
3400
3401
3402
3403
3404
3405
3406
3407
3408
3409
3410
3411
3412
3413
3414
3415
3416
3417
3418
3419
3420
3421
3422
3423
3424
3425
3426
3427
3428
3429
3430
3431
3432
3433
3434
3435
3436
3437
3438
3439
3440
3441
3442
3443
3444
3445
3446
3447
3448
3449
3450
3451
3452
3453
3454
3455
3456
3457
3458
3459
3460
3461
3462
3463
3464
3465
3466
3467
3468
3469
3470
3471
3472
3473
3474
3475
3476
3477
3478
3479
3480
3481
3482
3483
3484
3485
3486
3487
3488
3489
3490
3491
3492
3493
3494
3495
3496
3497
3498
3499
3500
3501
3502
3503
3504
3505
3506
3507
3508
3509
3510
3511
3512
3513
3514
3515
3516
3517
3518
3519
3520
3521
3522
3523
3524
3525
3526
3527
3528
3529
3530
3531
3532
3533
3534
3535
3536
3537
3538
3539
3540
3541
3542
3543
3544
3545
3546
3547
3548
3549
3550
3551
3552
3553
3554
3555
3556
3557
3558
3559
3560
3561
3562
3563
3564
3565
3566
3567
3568
3569
3570
3571
3572
3573
3574
3575
3576
3577
3578
3579
3580
3581
3582
3583
3584
3585
3586
3587
3588
3589
3590
3591
3592
3593
3594
3595
3596
3597
3598
3599
3600
3601
3602
3603
3604
3605
3606
3607
3608
3609
3610
3611
3612
3613
3614
3615
3616
3617
3618
3619
3620
3621
3622
3623
3624
3625
3626
3627
3628
3629
3630
3631
3632
3633
3634
3635
3636
3637
3638
3639
3640
3641
3642
3643
3644
3645
3646
3647
3648
3649
3650
3651
3652
3653
3654
3655
3656
3657
3658
3659
3660
3661
3662
3663
3664
3665
3666
3667
3668
3669
3670
3671
3672
3673
3674
3675
3676
3677
3678
3679
3680
3681
3682
3683
3684
3685
3686
3687
3688
3689
3690
3691
3692
3693
3694
3695
3696
3697
3698
3699
3700
3701
3702
3703
3704
3705
3706
3707
3708
3709
3710
3711
3712
3713
3714
3715
3716
3717
3718
3719
3720
3721
3722
3723
3724
3725
3726
3727
3728
3729
3730
3731
3732
3733
3734
3735
3736
3737
3738
3739
3740
3741
3742
3743
3744
3745
3746
3747
3748
3749
3750
3751
3752
3753
3754
3755
3756
3757
3758
3759
3760
3761
3762
3763
3764
3765
3766
3767
3768
3769
3770
3771
3772
3773
3774
3775
3776
3777
3778
3779
3780
3781
3782
3783
3784
3785
3786
3787
3788
3789
3790
3791
3792
3793
3794
3795
3796
3797
3798
3799
3800
3801
3802
3803
3804
3805
3806
3807
3808
3809
3810
3811
3812
3813
3814
3815
3816
3817
3818
3819
3820
3821
3822
3823
3824
3825
3826
3827
3828
3829
3830
3831
3832
3833
3834
3835
3836
3837
3838
3839
3840
3841
3842
3843
3844
3845
3846
3847
3848
3849
3850
3851
3852
3853
3854
3855
3856
3857
3858
3859
3860
3861
3862
3863
3864
3865
3866
3867
3868
3869
3870
3871
3872
3873
3874
3875
3876
3877
3878
3879
3880
3881
3882
3883
3884
3885
3886
3887
3888
3889
3890
3891
3892
3893
3894
3895
3896
3897
3898
3899
3900
3901
3902
3903
3904
3905
3906
3907
3908
3909
3910
3911
3912
3913
3914
3915
3916
3917
3918
3919
3920
3921
3922
3923
3924
3925
3926
3927
3928
3929
3930
3931
3932
3933
3934
3935
3936
3937
3938
3939
3940
3941
3942
3943
3944
3945
3946
3947
3948
3949
3950
3951
3952
3953
3954
3955
3956
3957
3958
3959
3960
3961
3962
3963
3964
3965
3966
3967
3968
3969
3970
3971
3972
3973
3974
3975
3976
3977
3978
3979
3980
3981
3982
3983
3984
3985
3986
3987
3988
3989
3990
3991
3992
3993
3994
3995
3996
3997
3998
3999
4000
4001
4002
4003
4004
4005
4006
4007
4008
4009
4010
4011
4012
4013
4014
4015
4016
4017
4018
4019
4020
4021
4022
4023
4024
4025
4026
4027
4028
4029
4030
4031
4032
4033
4034
4035
4036
4037
4038
4039
4040
4041
4042
4043
4044
4045
4046
4047
4048
4049
4050
4051
4052
4053
4054
4055
4056
4057
4058
4059
4060
4061
4062
4063
4064
4065
4066
4067
4068
4069
4070
4071
4072
4073
4074
4075
4076
4077
4078
4079
4080
4081
4082
4083
4084
4085
4086
4087
4088
4089
4090
4091
4092
4093
4094
4095
4096
4097
4098
4099
4100
4101
4102
4103
4104
4105
4106
4107
4108
4109
4110
4111
4112
4113
4114
4115
4116
4117
4118
4119
4120
4121
4122
4123
4124
4125
4126
4127
4128
4129
4130
4131
4132
4133
4134
4135
4136
4137
4138
4139
4140
4141
4142
4143
4144
4145
4146
4147
4148
4149
4150
4151
4152
4153
4154
4155
4156
4157
4158
4159
4160
4161
4162
4163
4164
4165
4166
4167
4168
4169
4170
4171
4172
4173
4174
4175
4176
4177
4178
4179
4180
4181
4182
4183
4184
4185
4186
4187
4188
4189
4190
4191
4192
4193
4194
4195
4196
4197
4198
4199
4200
4201
4202
4203
4204
4205
4206
4207
4208
4209
4210
4211
4212
4213
4214
4215
4216
4217
4218
4219
4220
4221
4222
4223
4224
4225
4226
4227
4228
4229
4230
4231
4232
4233
4234
4235
4236
4237
4238
4239
4240
4241
4242
4243
4244
4245
4246
4247
4248
4249
4250
4251
4252
4253
4254
4255
4256
4257
4258
4259
4260
4261
4262
4263
4264
4265
4266
4267
4268
4269
4270
4271
4272
4273
4274
4275
4276
4277
4278
4279
4280
4281
4282
4283
4284
4285
4286
4287
4288
4289
4290
4291
4292
4293
4294
4295
4296
4297
4298
4299
4300
4301
4302
4303
4304
4305
4306
4307
4308
4309
4310
4311
4312
4313
4314
4315
4316
4317
4318
4319
4320
4321
4322
4323
4324
4325
4326
4327
4328
4329
4330
4331
4332
4333
4334
4335
4336
4337
4338
4339
4340
4341
4342
4343
4344
4345
4346
4347
4348
4349
4350
4351
4352
4353
4354
4355
4356
4357
4358
4359
4360
4361
4362
4363
4364
4365
4366
4367
4368
4369
4370
4371
4372
4373
4374
4375
4376
4377
4378
4379
4380
4381
4382
4383
4384
4385
4386
4387
4388
4389
4390
4391
4392
4393
4394
4395
4396
4397
4398
4399
4400
4401
4402
4403
4404
4405
4406
4407
4408
4409
4410
4411
4412
4413
4414
4415
4416
4417
4418
4419
4420
4421
4422
4423
4424
4425
4426
4427
4428
4429
4430
4431
4432
4433
4434
4435
4436
4437
4438
4439
4440
4441
4442
4443
4444
4445
4446
4447
4448
4449
4450
4451
4452
4453
4454
4455
4456
4457
4458
4459
4460
4461
4462
4463
4464
4465
4466
4467
4468
4469
4470
4471
4472
4473
4474
4475
4476
4477
4478
4479
4480
4481
4482
4483
4484
4485
4486
4487
4488
4489
4490
4491
4492
4493
4494
4495
4496
4497
4498
4499
4500
4501
4502
4503
4504
4505
4506
4507
4508
4509
4510
4511
4512
4513
4514
4515
4516
4517
4518
4519
4520
4521
4522
4523
4524
4525
4526
4527
4528
4529
4530
4531
4532
4533
4534
4535
4536
4537
4538
4539
4540
4541
4542
4543
4544
4545
4546
4547
4548
4549
4550
4551
4552
4553
4554
4555
4556
4557
4558
4559
4560
4561
4562
4563
4564
4565
4566
4567
4568
4569
4570
4571
4572
4573
4574
4575
4576
4577
4578
4579
4580
4581
4582
4583
4584
4585
4586
4587
4588
4589
4590
4591
4592
4593
4594
4595
4596
4597
4598
4599
4600
4601
4602
4603
4604
4605
4606
4607
4608
4609
4610
4611
4612
4613
4614
4615
4616
4617
4618
4619
4620
4621
4622
4623
4624
4625
4626
4627
4628
4629
4630
4631
4632
4633
4634
4635
4636
4637
4638
4639
4640
4641
4642
4643
4644
4645
4646
4647
4648
4649
4650
4651
4652
4653
4654
4655
4656
4657
4658
4659
4660
4661
4662
4663
4664
4665
4666
4667
4668
4669
4670
4671
4672
4673
4674
4675
4676
4677
4678
4679
4680
4681
4682
4683
4684
4685
4686
4687
4688
4689
4690
4691
4692
4693
4694
4695
4696
4697
4698
4699
4700
4701
4702
4703
4704
4705
4706
4707
4708
4709
4710
4711
4712
4713
4714
4715
4716
4717
4718
4719
4720
4721
4722
4723
4724
4725
4726
4727
4728
4729
4730
4731
4732
4733
4734
4735
4736
4737
4738
4739
4740
4741
4742
4743
4744
4745
4746
4747
4748
4749
4750
4751
4752
4753
4754
4755
4756
4757
4758
4759
4760
4761
4762
4763
4764
4765
4766
4767
4768
4769
4770
4771
4772
4773
4774
4775
4776
4777
4778
4779
4780
4781
4782
4783
4784
4785
4786
4787
4788
4789
4790
4791
4792
4793
4794
4795
4796
4797
4798
4799
4800
4801
4802
4803
4804
4805
4806
4807
4808
4809
4810
4811
4812
4813
4814
4815
4816
4817
4818
4819
4820
4821
4822
4823
4824
4825
4826
4827
4828
4829
4830
4831
4832
4833
4834
4835
4836
4837
4838
4839
4840
4841
4842
4843
4844
4845
4846
4847
4848
4849
4850
4851
4852
4853
4854
4855
4856
4857
4858
4859
4860
4861
4862
4863
4864
4865
4866
4867
4868
4869
4870
4871
4872
4873
4874
4875
4876
4877
4878
4879
4880
4881
4882
4883
4884
4885
4886
4887
4888
4889
4890
4891
4892
4893
4894
4895
4896
4897
4898
4899
4900
4901
4902
4903
4904
4905
4906
4907
4908
4909
4910
4911
4912
4913
4914
4915
4916
4917
4918
4919
4920
4921
4922
4923
4924
4925
4926
4927
4928
4929
4930
4931
4932
4933
4934
4935
4936
4937
4938
4939
4940
4941
4942
4943
4944
4945
4946
4947
4948
4949
4950
4951
4952
4953
4954
4955
4956
4957
4958
4959
4960
4961
4962
4963
4964
4965
4966
4967
4968
4969
4970
4971
4972
4973
4974
4975
4976
4977
4978
4979
4980
4981
4982
4983
4984
4985
4986
4987
4988
4989
4990
4991
4992
4993
4994
4995
4996
4997
4998
4999
5000
5001
5002
5003
5004
5005
5006
5007
5008
5009
5010
5011
5012
5013
5014
5015
5016
5017
5018
5019
5020
5021
5022
5023
5024
5025
5026
5027
5028
5029
5030
5031
5032
5033
5034
5035
5036
5037
5038
5039
5040
5041
5042
5043
5044
5045
5046
5047
5048
5049
5050
5051
5052
5053
5054
5055
5056
5057
5058
5059
5060
5061
5062
5063
5064
5065
5066
5067
5068
5069
5070
5071
5072
5073
5074
5075
5076
5077
5078
5079
5080
5081
5082
5083
5084
5085
5086
5087
5088
5089
5090
5091
5092
5093
5094
5095
5096
5097
5098
5099
5100
5101
5102
5103
5104
5105
5106
5107
5108
5109
5110
5111
5112
5113
5114
5115
5116
5117
5118
5119
5120
5121
5122
5123
5124
5125
5126
5127
5128
5129
5130
5131
5132
5133
5134
5135
5136
5137
5138
5139
5140
5141
5142
5143
5144
5145
5146
5147
5148
5149
5150
5151
5152
5153
5154
5155
5156
5157
5158
5159
5160
5161
5162
5163
5164
5165
5166
5167
5168
5169
5170
5171
5172
5173
5174
5175
5176
5177
5178
5179
5180
5181
5182
5183
5184
5185
5186
5187
5188
5189
5190
5191
5192
5193
5194
5195
5196
5197
5198
5199
5200
5201
5202
5203
5204
5205
5206
5207
5208
5209
5210
5211
5212
5213
5214
5215
5216
5217
5218
5219
5220
5221
5222
5223
5224
5225
5226
5227
5228
5229
5230
5231
5232
5233
5234
5235
5236
5237
5238
5239
5240
5241
5242
5243
5244
5245
5246
5247
5248
5249
5250
5251
5252
5253
5254
5255
5256
5257
5258
5259
5260
5261
5262
5263
5264
5265
5266
5267
5268
5269
5270
5271
5272
5273
5274
5275
5276
5277
5278
5279
5280
5281
5282
5283
5284
5285
5286
5287
5288
5289
5290
5291
5292
5293
5294
5295
5296
5297
5298
5299
5300
5301
5302
5303
5304
5305
5306
5307
5308
5309
5310
5311
5312
5313
5314
5315
5316
5317
5318
5319
5320
5321
5322
5323
5324
5325
5326
5327
5328
5329
5330
5331
5332
5333
5334
5335
5336
5337
5338
5339
5340
5341
5342
5343
5344
5345
5346
5347
5348
5349
5350
5351
5352
5353
5354
5355
5356
5357
5358
5359
5360
5361
5362
5363
5364
5365
5366
5367
5368
5369
5370
5371
5372
5373
5374
5375
5376
5377
5378
5379
5380
5381
5382
5383
5384
5385
5386
5387
5388
5389
5390
5391
5392
5393
5394
5395
5396
5397
5398
5399
5400
5401
5402
5403
5404
5405
5406
5407
5408
5409
5410
5411
5412
5413
5414
5415
5416
5417
5418
5419
5420
5421
5422
5423
5424
5425
5426
5427
5428
5429
5430
5431
5432
5433
5434
5435
5436
5437
5438
5439
5440
5441
5442
5443
5444
5445
5446
5447
5448
5449
5450
5451
5452
5453
5454
5455
5456
5457
5458
5459
5460
5461
5462
5463
5464
5465
5466
5467
5468
5469
5470
5471
5472
5473
5474
5475
5476
5477
5478
5479
5480
5481
5482
5483
5484
5485
5486
5487
5488
5489
5490
5491
5492
5493
5494
5495
5496
5497
5498
5499
5500
5501
5502
5503
5504
5505
5506
5507
5508
5509
5510
5511
5512
5513
5514
5515
5516
5517
5518
5519
5520
5521
5522
5523
5524
5525
5526
5527
5528
5529
5530
5531
5532
5533
5534
5535
5536
5537
5538
5539
5540
5541
5542
5543
5544
5545
5546
5547
5548
5549
5550
5551
5552
5553
5554
5555
5556
5557
5558
5559
5560
5561
5562
5563
5564
5565
5566
5567
5568
5569
5570
5571
5572
5573
5574
5575
5576
5577
5578
5579
5580
5581
5582
5583
5584
5585
5586
5587
5588
5589
5590
5591
5592
5593
5594
5595
5596
5597
5598
5599
5600
5601
5602
5603
5604
5605
5606
5607
5608
5609
5610
5611
5612
5613
5614
5615
5616
5617
5618
5619
5620
5621
5622
5623
5624
5625
5626
5627
5628
5629
5630
5631
5632
5633
5634
5635
5636
5637
5638
5639
5640
5641
5642
5643
5644
5645
5646
5647
5648
5649
5650
5651
5652
5653
5654
5655
5656
5657
5658
5659
5660
5661
5662
5663
5664
5665
5666
5667
5668
5669
5670
5671
5672
5673
5674
5675
5676
5677
5678
5679
5680
5681
5682
5683
5684
5685
5686
5687
5688
5689
5690
5691
5692
5693
5694
5695
5696
5697
5698
5699
5700
5701
5702
5703
5704
5705
5706
5707
5708
5709
5710
5711
5712
5713
5714
5715
5716
5717
5718
5719
5720
5721
5722
5723
5724
5725
5726
5727
5728
5729
5730
5731
5732
5733
5734
5735
5736
5737
5738
5739
5740
5741
5742
5743
5744
5745
5746
5747
5748
5749
5750
5751
5752
5753
5754
5755
5756
5757
5758
5759
5760
5761
5762
5763
5764
5765
5766
5767
5768
5769
5770
5771
5772
5773
5774
5775
5776
5777
5778
5779
5780
5781
5782
5783
5784
5785
5786
5787
5788
5789
5790
5791
5792
5793
5794
5795
5796
5797
5798
5799
5800
5801
5802
5803
5804
5805
5806
5807
5808
5809
5810
5811
5812
5813
5814
5815
5816
5817
5818
5819
5820
5821
5822
5823
5824
5825
5826
5827
5828
5829
5830
5831
5832
5833
5834
5835
5836
5837
5838
5839
5840
5841
5842
5843
5844
5845
5846
5847
5848
5849
5850
5851
5852
5853
5854
5855
5856
5857
5858
5859
5860
5861
5862
5863
5864
5865
5866
5867
5868
5869
5870
5871
5872
5873
5874
5875
5876
5877
5878
5879
5880
5881
5882
5883
5884
5885
5886
5887
5888
5889
5890
5891
5892
5893
5894
5895
5896
5897
5898
5899
5900
5901
5902
5903
5904
5905
5906
5907
5908
5909
5910
5911
5912
5913
5914
5915
5916
5917
5918
5919
5920
5921
5922
5923
5924
5925
5926
5927
5928
5929
5930
5931
5932
5933
5934
5935
5936
5937
5938
5939
5940
5941
5942
5943
5944
5945
5946
5947
5948
5949
5950
5951
5952
5953
5954
5955
5956
5957
5958
5959
5960
5961
5962
5963
5964
5965
5966
5967
5968
5969
5970
5971
5972
5973
5974
5975
5976
5977
5978
5979
5980
5981
5982
5983
5984
5985
5986
5987
5988
5989
5990
5991
5992
5993
5994
5995
5996
5997
5998
5999
6000
6001
6002
6003
6004
6005
6006
6007
6008
6009
6010
6011
6012
6013
6014
6015
6016
6017
6018
6019
6020
6021
6022
6023
6024
6025
6026
6027
6028
6029
6030
6031
6032
6033
6034
6035
6036
6037
6038
6039
6040
6041
6042
6043
6044
6045
6046
6047
6048
6049
6050
6051
6052
6053
6054
6055
6056
6057
6058
6059
6060
6061
6062
6063
6064
6065
6066
6067
6068
6069
6070
6071
6072
6073
6074
6075
6076
6077
6078
6079
6080
6081
6082
6083
6084
6085
6086
6087
6088
6089
6090
6091
6092
6093
6094
6095
6096
6097
6098
6099
6100
6101
6102
6103
6104
6105
6106
6107
6108
6109
6110
6111
6112
6113
6114
6115
6116
6117
6118
6119
6120
6121
6122
6123
6124
6125
6126
6127
6128
6129
6130
6131
6132
6133
6134
6135
6136
6137
6138
6139
6140
6141
6142
6143
6144
6145
6146
6147
6148
6149
6150
6151
6152
6153
6154
6155
6156
6157
6158
6159
6160
6161
6162
6163
6164
6165
6166
6167
6168
6169
6170
6171
6172
6173
6174
6175
6176
6177
6178
6179
6180
6181
6182
6183
6184
6185
6186
6187
6188
6189
6190
6191
6192
6193
6194
6195
6196
6197
6198
6199
6200
6201
6202
6203
6204
6205
6206
6207
6208
6209
6210
6211
6212
6213
6214
6215
6216
6217
6218
6219
6220
6221
6222
6223
6224
6225
6226
6227
6228
6229
6230
6231
6232
6233
6234
6235
6236
6237
6238
6239
6240
6241
6242
6243
6244
6245
6246
6247
6248
6249
6250
6251
6252
6253
6254
6255
6256
6257
6258
6259
6260
6261
6262
6263
6264
6265
6266
6267
6268
6269
6270
6271
6272
6273
6274
6275
6276
6277
6278
6279
6280
6281
6282
6283
6284
6285
6286
6287
6288
6289
6290
6291
6292
6293
6294
6295
6296
6297
6298
6299
6300
6301
6302
6303
6304
6305
6306
6307
6308
6309
6310
6311
6312
6313
6314
6315
6316
6317
6318
6319
6320
6321
6322
6323
6324
6325
6326
6327
6328
6329
6330
6331
6332
6333
6334
6335
6336
6337
6338
6339
6340
6341
6342
6343
6344
6345
6346
6347
6348
6349
6350
6351
6352
6353
6354
6355
6356
6357
6358
6359
6360
6361
6362
6363
6364
6365
6366
6367
6368
6369
6370
6371
6372
6373
6374
6375
6376
6377
6378
6379
6380
6381
6382
6383
6384
6385
6386
6387
6388
6389
6390
6391
6392
6393
6394
6395
6396
6397
6398
6399
6400
6401
6402
6403
6404
6405
6406
6407
6408
6409
6410
6411
6412
6413
6414
6415
6416
6417
6418
6419
6420
6421
6422
6423
6424
6425
6426
6427
6428
6429
6430
6431
6432
6433
6434
6435
6436
6437
6438
6439
6440
6441
6442
6443
6444
6445
6446
6447
6448
6449
6450
6451
6452
6453
6454
6455
6456
6457
6458
6459
6460
6461
6462
6463
6464
6465
6466
6467
6468
6469
6470
6471
6472
6473
6474
6475
6476
6477
6478
6479
6480
6481
6482
6483
6484
6485
6486
6487
6488
6489
6490
6491
6492
6493
6494
6495
6496
6497
6498
6499
6500
6501
6502
6503
6504
6505
6506
6507
6508
6509
6510
6511
6512
6513
6514
6515
6516
6517
6518
6519
6520
6521
6522
6523
6524
6525
6526
6527
6528
6529
6530
6531
6532
6533
6534
6535
6536
6537
6538
6539
6540
6541
6542
6543
6544
6545
6546
6547
6548
6549
6550
6551
6552
6553
6554
6555
6556
6557
6558
6559
6560
6561
6562
6563
6564
6565
6566
6567
6568
6569
6570
6571
6572
6573
6574
6575
6576
6577
6578
6579
6580
6581
6582
6583
6584
6585
6586
6587
6588
6589
6590
6591
6592
6593
6594
6595
6596
6597
6598
6599
6600
6601
6602
6603
6604
6605
6606
6607
6608
6609
6610
6611
6612
6613
6614
6615
6616
6617
6618
6619
6620
6621
6622
6623
6624
6625
6626
6627
6628
6629
6630
6631
6632
6633
6634
6635
6636
6637
6638
6639
6640
6641
6642
6643
6644
6645
6646
6647
6648
6649
6650
6651
6652
6653
6654
6655
6656
6657
6658
6659
6660
6661
6662
6663
6664
6665
6666
6667
6668
6669
6670
6671
6672
6673
6674
6675
6676
6677
6678
6679
6680
6681
6682
6683
6684
6685
6686
6687
6688
6689
6690
6691
6692
6693
6694
6695
6696
6697
6698
6699
6700
6701
6702
6703
6704
6705
6706
6707
6708
6709
6710
6711
6712
6713
6714
6715
6716
6717
6718
6719
6720
6721
6722
6723
6724
6725
6726
6727
6728
6729
6730
6731
6732
6733
6734
6735
6736
6737
6738
6739
6740
6741
6742
6743
6744
6745
6746
6747
6748
6749
6750
6751
6752
6753
6754
6755
6756
6757
6758
6759
6760
6761
6762
6763
6764
6765
6766
6767
6768
6769
6770
6771
6772
6773
6774
6775
6776
6777
6778
6779
6780
6781
6782
6783
6784
6785
6786
6787
6788
6789
6790
6791
6792
6793
6794
6795
6796
6797
6798
6799
6800
6801
6802
6803
6804
6805
6806
6807
6808
6809
6810
6811
6812
6813
6814
6815
6816
6817
6818
6819
6820
6821
6822
6823
6824
6825
6826
6827
6828
6829
6830
6831
6832
6833
6834
6835
6836
6837
6838
6839
6840
6841
6842
6843
6844
6845
6846
6847
6848
6849
6850
6851
6852
6853
6854
6855
6856
6857
6858
6859
6860
6861
6862
6863
6864
6865
6866
6867
6868
6869
6870
6871
6872
6873
6874
6875
6876
6877
6878
6879
6880
6881
6882
6883
6884
6885
6886
6887
6888
6889
6890
6891
6892
6893
6894
6895
6896
6897
6898
6899
6900
6901
6902
6903
6904
6905
6906
6907
6908
6909
6910
6911
6912
6913
6914
6915
6916
6917
6918
6919
6920
6921
6922
6923
6924
6925
6926
6927
6928
6929
6930
6931
6932
6933
6934
6935
6936
6937
6938
6939
6940
6941
6942
6943
6944
6945
6946
6947
6948
6949
6950
6951
6952
6953
6954
6955
6956
6957
6958
6959
6960
6961
6962
6963
6964
6965
6966
6967
6968
6969
6970
6971
6972
6973
6974
6975
6976
6977
6978
6979
6980
6981
6982
6983
6984
6985
6986
6987
6988
6989
6990
6991
6992
6993
6994
6995
6996
6997
6998
6999
7000
7001
7002
7003
7004
7005
7006
7007
7008
7009
7010
7011
7012
7013
7014
7015
7016
7017
7018
7019
7020
7021
7022
7023
7024
7025
7026
7027
7028
7029
7030
7031
7032
7033
7034
7035
7036
7037
7038
7039
7040
7041
7042
7043
7044
7045
7046
7047
7048
7049
7050
7051
7052
7053
7054
7055
7056
7057
7058
7059
7060
7061
7062
7063
7064
7065
7066
7067
7068
7069
7070
7071
7072
7073
7074
7075
7076
7077
7078
7079
7080
7081
7082
7083
7084
7085
7086
7087
7088
7089
7090
7091
7092
7093
7094
7095
7096
7097
7098
7099
7100
7101
7102
7103
7104
7105
7106
7107
7108
7109
7110
7111
7112
7113
7114
7115
7116
7117
7118
7119
7120
7121
7122
7123
7124
7125
7126
7127
7128
7129
7130
7131
7132
7133
7134
7135
7136
7137
7138
7139
7140
7141
7142
7143
7144
7145
7146
7147
7148
7149
7150
7151
7152
7153
7154
7155
7156
7157
7158
7159
7160
7161
7162
7163
7164
7165
7166
7167
7168
7169
7170
7171
7172
7173
7174
7175
7176
7177
7178
7179
7180
7181
7182
7183
7184
7185
7186
7187
7188
7189
7190
7191
7192
7193
7194
7195
7196
7197
7198
7199
7200
7201
7202
7203
7204
7205
7206
7207
7208
7209
7210
7211
7212
7213
7214
7215
7216
7217
7218
7219
7220
7221
7222
7223
7224
7225
7226
7227
7228
7229
7230
7231
7232
7233
7234
7235
7236
7237
7238
7239
7240
7241
7242
7243
7244
7245
7246
7247
7248
7249
7250
7251
7252
7253
7254
7255
7256
7257
7258
7259
7260
7261
7262
7263
7264
7265
7266
7267
7268
7269
7270
7271
7272
7273
7274
7275
7276
7277
7278
7279
7280
7281
7282
7283
7284
7285
7286
7287
7288
7289
7290
7291
7292
7293
7294
7295
7296
7297
7298
7299
7300
7301
7302
7303
7304
7305
7306
7307
7308
7309
7310
7311
7312
7313
7314
7315
7316
7317
7318
7319
7320
7321
7322
7323
7324
7325
7326
7327
7328
7329
7330
7331
7332
7333
7334
7335
7336
7337
7338
7339
7340
7341
7342
7343
7344
7345
7346
7347
7348
7349
7350
7351
7352
7353
7354
7355
7356
7357
7358
7359
7360
7361
7362
7363
7364
7365
7366
7367
7368
7369
7370
7371
7372
7373
7374
7375
7376
7377
7378
7379
7380
7381
7382
7383
7384
7385
7386
7387
7388
7389
7390
7391
7392
7393
7394
7395
7396
7397
7398
7399
7400
7401
7402
7403
7404
7405
7406
7407
7408
7409
7410
7411
7412
7413
7414
7415
7416
7417
7418
7419
7420
7421
7422
7423
7424
7425
7426
7427
7428
7429
7430
7431
7432
7433
7434
7435
7436
7437
7438
7439
7440
7441
7442
7443
7444
7445
7446
7447
7448
7449
7450
7451
7452
7453
7454
7455
7456
7457
7458
7459
7460
7461
7462
7463
7464
7465
7466
7467
7468
7469
7470
7471
7472
7473
7474
7475
7476
7477
7478
7479
7480
7481
7482
7483
7484
7485
7486
7487
7488
7489
7490
7491
7492
7493
7494
7495
7496
7497
7498
7499
7500
7501
7502
7503
7504
7505
7506
7507
7508
7509
7510
7511
7512
7513
7514
7515
7516
7517
7518
7519
7520
7521
7522
7523
7524
7525
7526
7527
7528
7529
7530
7531
7532
7533
7534
7535
7536
7537
7538
7539
7540
7541
7542
7543
7544
7545
7546
7547
7548
7549
7550
7551
7552
7553
7554
7555
7556
7557
7558
7559
7560
7561
7562
7563
7564
7565
7566
7567
7568
7569
7570
7571
7572
7573
7574
7575
7576
7577
7578
7579
7580
7581
7582
7583
7584
7585
7586
7587
7588
7589
7590
7591
7592
7593
7594
7595
7596
7597
7598
7599
7600
7601
7602
7603
7604
7605
7606
7607
7608
7609
7610
7611
7612
7613
7614
7615
7616
7617
7618
7619
7620
7621
7622
7623
7624
7625
7626
7627
7628
7629
7630
7631
7632
7633
7634
7635
7636
7637
7638
7639
7640
7641
7642
7643
7644
7645
7646
7647
7648
7649
7650
7651
7652
7653
7654
7655
7656
7657
7658
7659
7660
7661
7662
7663
7664
7665
7666
7667
7668
7669
7670
7671
7672
7673
7674
7675
7676
7677
7678
7679
7680
7681
7682
7683
7684
7685
7686
7687
7688
7689
7690
7691
7692
7693
7694
7695
7696
7697
7698
7699
7700
7701
7702
7703
7704
7705
7706
7707
7708
7709
7710
7711
7712
7713
7714
7715
7716
7717
7718
7719
7720
7721
7722
7723
7724
7725
7726
7727
7728
7729
7730
7731
7732
7733
7734
7735
7736
7737
7738
7739
7740
7741
7742
7743
7744
7745
7746
7747
7748
7749
7750
7751
7752
7753
7754
7755
7756
7757
7758
7759
7760
7761
7762
7763
7764
7765
7766
7767
7768
7769
7770
7771
7772
7773
7774
7775
7776
7777
7778
7779
7780
7781
7782
7783
7784
7785
7786
7787
7788
7789
7790
7791
7792
7793
7794
7795
7796
7797
7798
7799
7800
7801
7802
7803
7804
7805
7806
7807
7808
7809
7810
7811
7812
7813
7814
7815
7816
7817
7818
7819
7820
7821
7822
7823
7824
7825
7826
7827
7828
7829
7830
7831
7832
7833
7834
7835
7836
7837
7838
7839
7840
7841
7842
7843
7844
7845
7846
7847
7848
7849
7850
7851
7852
7853
7854
7855
7856
7857
7858
7859
7860
7861
7862
7863
7864
7865
7866
7867
7868
7869
7870
7871
7872
7873
7874
7875
7876
7877
7878
7879
7880
7881
7882
7883
7884
7885
7886
7887
7888
7889
7890
7891
7892
7893
7894
7895
7896
7897
7898
7899
7900
7901
7902
7903
7904
7905
7906
7907
7908
7909
7910
7911
7912
7913
7914
7915
7916
7917
7918
7919
7920
7921
7922
7923
7924
7925
7926
7927
7928
7929
7930
7931
7932
7933
7934
7935
7936
7937
7938
7939
7940
7941
7942
7943
7944
7945
7946
7947
7948
7949
7950
7951
7952
7953
7954
7955
7956
7957
7958
7959
7960
7961
7962
7963
7964
7965
7966
7967
7968
7969
7970
7971
7972
7973
7974
7975
7976
7977
7978
7979
7980
7981
7982
7983
7984
7985
7986
7987
7988
7989
7990
7991
7992
7993
7994
7995
7996
7997
7998
7999
8000
8001
8002
8003
8004
8005
8006
8007
8008
8009
8010
8011
8012
8013
8014
8015
8016
8017
8018
8019
8020
8021
8022
8023
8024
8025
8026
8027
8028
8029
8030
8031
8032
8033
8034
8035
8036
8037
8038
8039
8040
8041
8042
8043
8044
8045
8046
8047
8048
8049
8050
8051
8052
8053
8054
8055
8056
8057
8058
8059
8060
8061
8062
8063
8064
8065
8066
8067
8068
8069
8070
8071
8072
8073
8074
8075
8076
8077
8078
8079
8080
8081
8082
8083
8084
8085
8086
8087
8088
8089
8090
8091
8092
8093
8094
8095
8096
8097
8098
8099
8100
8101
8102
8103
8104
8105
8106
8107
8108
8109
8110
8111
8112
8113
8114
8115
8116
8117
8118
8119
8120
8121
8122
8123
8124
8125
8126
8127
8128
8129
8130
8131
8132
8133
8134
8135
8136
8137
8138
8139
8140
8141
8142
8143
8144
8145
8146
8147
8148
8149
8150
8151
8152
8153
8154
8155
8156
8157
8158
8159
8160
8161
8162
8163
8164
8165
8166
8167
8168
8169
8170
8171
8172
8173
8174
8175
8176
8177
8178
8179
8180
8181
8182
8183
8184
8185
8186
8187
8188
8189
8190
8191
8192
8193
8194
8195
8196
8197
8198
8199
8200
8201
8202
8203
8204
8205
8206
8207
8208
8209
8210
8211
8212
8213
8214
8215
8216
8217
8218
8219
8220
8221
8222
8223
8224
8225
8226
8227
8228
8229
8230
8231
8232
8233
8234
8235
8236
8237
8238
8239
8240
8241
8242
8243
8244
8245
8246
8247
8248
8249
8250
8251
8252
8253
8254
8255
8256
8257
8258
8259
8260
8261
8262
8263
8264
8265
8266
8267
8268
8269
8270
8271
8272
8273
8274
8275
8276
8277
8278
8279
8280
8281
8282
8283
8284
8285
8286
8287
8288
8289
8290
8291
8292
8293
8294
8295
8296
8297
8298
8299
8300
8301
8302
8303
8304
8305
8306
8307
8308
8309
8310
8311
8312
8313
8314
8315
8316
8317
8318
8319
8320
8321
8322
8323
8324
8325
<!-- doc/src/sgml/config.sgml -->

<chapter id="runtime-config">
  <title>Server Configuration</title>

  <indexterm>
   <primary>configuration</primary>
   <secondary>of the server</secondary>
  </indexterm>

  <para>
   There are many configuration parameters that affect the behavior of
   the database system. In the first section of this chapter we
   describe how to interact with configuration parameters. The subsequent sections
   discuss each parameter in detail.
  </para>

  <sect1 id="config-setting">
   <title>Setting Parameters</title>

   <sect2 id="config-setting-names-values">
    <title>Parameter Names and Values</title>

    <para>
     All parameter names are case-insensitive. Every parameter takes a
     value of one of five types: boolean, string, integer, floating point,
     or enumerated (enum).  The type determines the syntax for setting the
     parameter:
    </para>

    <itemizedlist>
     <listitem>
      <para>
       <emphasis>Boolean:</emphasis>
       Values can be written as
       <literal>on</literal>,
       <literal>off</literal>,
       <literal>true</literal>,
       <literal>false</literal>,
       <literal>yes</literal>,
       <literal>no</literal>,
       <literal>1</literal>,
       <literal>0</literal>
       (all case-insensitive) or any unambiguous prefix of one of these.
      </para>
     </listitem>

     <listitem>
      <para>
       <emphasis>String:</emphasis>
       In general, enclose the value in single quotes, doubling any single
       quotes within the value.  Quotes can usually be omitted if the value
       is a simple number or identifier, however.
      </para>
     </listitem>

     <listitem>
      <para>
       <emphasis>Numeric (integer and floating point):</emphasis>
       A decimal point is permitted only for floating-point parameters.
       Do not use thousands separators.  Quotes are not required.
      </para>
     </listitem>

     <listitem>
      <para>
       <emphasis>Numeric with Unit:</emphasis>
       Some numeric parameters have an implicit unit, because they describe
       quantities of memory or time. The unit might be kilobytes, blocks
       (typically eight kilobytes), milliseconds, seconds, or minutes.
       An unadorned numeric value for one of these settings will use the
       setting's default unit, which can be learned from
       <structname>pg_settings</>.<structfield>unit</>.
       For convenience, settings can be given with a unit specified explicitly,
       for example <literal>'120 ms'</> for a time value, and they will be
       converted to whatever the parameter's actual unit is.  Note that the
       value must be written as a string (with quotes) to use this feature.
       The unit name is case-sensitive, and there can be whitespace between
       the numeric value and the unit.

       <itemizedlist>
        <listitem>
         <para>
          Valid memory units are <literal>kB</literal> (kilobytes),
          <literal>MB</literal> (megabytes), <literal>GB</literal>
          (gigabytes), and <literal>TB</literal> (terabytes).
          The multiplier for memory units is 1024, not 1000.
         </para>
        </listitem>

        <listitem>
         <para>
          Valid time units are <literal>ms</literal> (milliseconds),
          <literal>s</literal> (seconds), <literal>min</literal> (minutes),
          <literal>h</literal> (hours), and <literal>d</literal> (days).
         </para>
        </listitem>
       </itemizedlist>
      </para>
     </listitem>

     <listitem>
      <para>
       <emphasis>Enumerated:</emphasis>
       Enumerated-type parameters are written in the same way as string
       parameters, but are restricted to have one of a limited set of
       values.  The values allowable for such a parameter can be found from
       <structname>pg_settings</>.<structfield>enumvals</>.
       Enum parameter values are case-insensitive.
      </para>
     </listitem>
    </itemizedlist>
   </sect2>

   <sect2 id="config-setting-configuration-file">
    <title>Parameter Interaction via the Configuration File</title>

    <para>
     The most fundamental way to set these parameters is to edit the file
     <filename>postgresql.conf</><indexterm><primary>postgresql.conf</></>,
     which is normally kept in the data directory.  A default copy is
     installed when the database cluster directory is initialized.
     An example of what this file might look like is:
<programlisting>
# This is a comment
log_connections = yes
log_destination = 'syslog'
search_path = '"$user", public'
shared_buffers = 128MB
</programlisting>
     One parameter is specified per line. The equal sign between name and
     value is optional. Whitespace is insignificant (except within a quoted
     parameter value) and blank lines are
     ignored. Hash marks (<literal>#</literal>) designate the remainder
     of the line as a comment.  Parameter values that are not simple
     identifiers or numbers must be single-quoted.  To embed a single
     quote in a parameter value, write either two quotes (preferred)
     or backslash-quote.
    </para>

    <para>
     Parameters set in this way provide default values for the cluster.
     The settings seen by active sessions will be these values unless they
     are overridden.  The following sections describe ways in which the
     administrator or user can override these defaults.
    </para>

    <para>
     <indexterm>
      <primary>SIGHUP</primary>
     </indexterm>
     The configuration file is reread whenever the main server process
     receives a <systemitem>SIGHUP</> signal; this signal is most easily
     sent by running <literal>pg_ctl reload</> from the command line or by
     calling the SQL function <function>pg_reload_conf()</function>. The main
     server process also propagates this signal to all currently running
     server processes, so that existing sessions also adopt the new values
     (this will happen after they complete any currently-executing client
     command).  Alternatively, you can
     send the signal to a single server process directly.  Some parameters
     can only be set at server start; any changes to their entries in the
     configuration file will be ignored until the server is restarted.
     Invalid parameter settings in the configuration file are likewise
     ignored (but logged) during <systemitem>SIGHUP</> processing.
    </para>

    <para>
     In addition to <filename>postgresql.conf</>,
     a <productname>PostgreSQL</productname> data directory contains a file
     <filename>postgresql.auto.conf</><indexterm><primary>postgresql.auto.conf</></>,
     which has the same format as <filename>postgresql.conf</> but should
     never be edited manually.  This file holds settings provided through
     the <xref linkend="SQL-ALTERSYSTEM"> command.  This file is automatically
     read whenever <filename>postgresql.conf</> is, and its settings take
     effect in the same way.  Settings in <filename>postgresql.auto.conf</>
     override those in <filename>postgresql.conf</>.
    </para>

    <para>
     The system view
     <link linkend="view-pg-file-settings"><structname>pg_file_settings</structname></link>
     can be helpful for pre-testing changes to the configuration file, or for
     diagnosing problems if a <systemitem>SIGHUP</> signal did not have the
     desired effects.
    </para>
   </sect2>

   <sect2 id="config-setting-sql-command-interaction">
    <title>Parameter Interaction via SQL</title>

     <para>
      <productname>PostgreSQL</productname> provides three SQL
      commands to establish configuration defaults.
      The already-mentioned <xref linkend="SQL-ALTERSYSTEM"> command
      provides a SQL-accessible means of changing global defaults; it is
      functionally equivalent to editing <filename>postgresql.conf</>.
      In addition, there are two commands that allow setting of defaults
      on a per-database or per-role basis:
     </para>

     <itemizedlist>
     <listitem>
      <para>
       The <xref linkend="sql-alterdatabase"> command allows global
       settings to be overridden on a per-database basis.
      </para>
     </listitem>

     <listitem>
      <para>
       The <xref linkend="sql-alterrole"> command allows both global and
       per-database settings to be overridden with user-specific values.
      </para>
     </listitem>
    </itemizedlist>

     <para>
      Values set with <command>ALTER DATABASE</> and <command>ALTER ROLE</>
      are applied only when starting a fresh database session.  They
      override values obtained from the configuration files or server
      command line, and constitute defaults for the rest of the session.
      Note that some settings cannot be changed after server start, and
      so cannot be set with these commands (or the ones listed below).
    </para>

     <para>
      Once a client is connected to the database, <productname>PostgreSQL</>
      provides two additional SQL commands (and equivalent functions) to
      interact with session-local configuration settings:
    </para>

    <itemizedlist>
     <listitem>
     <para>
      The <xref linkend="SQL-SHOW"> command allows inspection of the
      current value of all parameters.  The corresponding function is
      <function>current_setting(setting_name text)</function>.
     </para>
     </listitem>

     <listitem>
      <para>
       The <xref linkend="SQL-SET"> command allows modification of the
       current value of those parameters that can be set locally to a
       session; it has no effect on other sessions.
       The corresponding function is
       <function>set_config(setting_name, new_value, is_local)</function>.
      </para>
     </listitem>
    </itemizedlist>

    <para>
     In addition, the system view <link
     linkend="view-pg-settings"><structname>pg_settings</></> can be
     used to view and change session-local values:
    </para>

    <itemizedlist>
     <listitem>
      <para>
       Querying this view is similar to using <command>SHOW ALL</> but
       provides more detail.  It is also more flexible, since it's possible
       to specify filter conditions or join against other relations.
      </para>
     </listitem>

     <listitem>
      <para>
       Using <xref linkend="SQL-UPDATE"> on this view, specifically
       updating the <structname>setting</> column, is the equivalent
       of issuing <command>SET</> commands.  For example, the equivalent of
<programlisting>
SET configuration_parameter TO DEFAULT;
</programlisting>
       is:
<programlisting>
UPDATE pg_settings SET setting = reset_val WHERE name = 'configuration_parameter';
</programlisting>
      </para>
     </listitem>
    </itemizedlist>

   </sect2>

   <sect2>
    <title>Parameter Interaction via the Shell</title>

     <para>
      In addition to setting global defaults or attaching
      overrides at the database or role level, you can pass settings to
      <productname>PostgreSQL</productname> via shell facilities.
      Both the server and <application>libpq</> client library
      accept parameter values via the shell.
     </para>

     <itemizedlist>
      <listitem>
      <para>
       During server startup, parameter settings can be
       passed to the <command>postgres</command> command via the
       <option>-c</> command-line parameter.  For example,
<programlisting>
postgres -c log_connections=yes -c log_destination='syslog'
</programlisting>
       Settings provided in this way override those set via
       <filename>postgresql.conf</> or <command>ALTER SYSTEM</>,
       so they cannot be changed globally without restarting the server.
     </para>
    </listitem>

    <listitem>
     <para>
      When starting a client session via <application>libpq</>,
      parameter settings can be
      specified using the <envar>PGOPTIONS</envar> environment variable.
      Settings established in this way constitute defaults for the life
      of the session, but do not affect other sessions.
      For historical reasons, the format of <envar>PGOPTIONS</envar> is
      similar to that used when launching the <command>postgres</command>
      command; specifically, the <option>-c</> flag must be specified.
      For example,
<programlisting>
env PGOPTIONS="-c geqo=off -c statement_timeout=5min" psql
</programlisting>
     </para>

     <para>
      Other clients and libraries might provide their own mechanisms,
      via the shell or otherwise, that allow the user to alter session
      settings without direct use of SQL commands.
     </para>
    </listitem>
   </itemizedlist>

   </sect2>

   <sect2 id="config-includes">
    <title>Managing Configuration File Contents</title>

     <para>
      <productname>PostgreSQL</> provides several features for breaking
      down complex <filename>postgresql.conf</> files into sub-files.
      These features are especially useful when managing multiple servers
      with related, but not identical, configurations.
     </para>

     <para>
      <indexterm>
       <primary><literal>include</></primary>
       <secondary>in configuration file</secondary>
      </indexterm>
      In addition to individual parameter settings,
      the <filename>postgresql.conf</> file can contain <firstterm>include
      directives</>, which specify another file to read and process as if
      it were inserted into the configuration file at this point.  This
      feature allows a configuration file to be divided into physically
      separate parts.  Include directives simply look like:
<programlisting>
include 'filename'
</programlisting>
      If the file name is not an absolute path, it is taken as relative to
      the directory containing the referencing configuration file.
      Inclusions can be nested.
     </para>

     <para>
      <indexterm>
       <primary><literal>include_if_exists</></primary>
       <secondary>in configuration file</secondary>
      </indexterm>
      There is also an <literal>include_if_exists</> directive, which acts
      the same as the <literal>include</> directive, except
      when the referenced file does not exist or cannot be read.  A regular
      <literal>include</> will consider this an error condition, but
      <literal>include_if_exists</> merely logs a message and continues
      processing the referencing configuration file.
     </para>

     <para>
      <indexterm>
       <primary><literal>include_dir</></primary>
       <secondary>in configuration file</secondary>
      </indexterm>
      The <filename>postgresql.conf</> file can also contain
      <literal>include_dir</literal> directives, which specify an entire
      directory of configuration files to include.  These look like
<programlisting>
include_dir 'directory'
</programlisting>
      Non-absolute directory names are taken as relative to the directory
      containing the referencing configuration file.  Within the specified
      directory, only non-directory files whose names end with the
      suffix <literal>.conf</literal> will be included.  File names that
      start with the <literal>.</literal> character are also ignored, to
      prevent mistakes since such files are hidden on some platforms.  Multiple
      files within an include directory are processed in file name order
      (according to C locale rules, i.e. numbers before letters, and
      uppercase letters before lowercase ones).
     </para>

     <para>
      Include files or directories can be used to logically separate portions
      of the database configuration, rather than having a single large
      <filename>postgresql.conf</> file.  Consider a company that has two
      database servers, each with a different amount of memory.  There are
      likely elements of the configuration both will share, for things such
      as logging.  But memory-related parameters on the server will vary
      between the two.  And there might be server specific customizations,
      too.  One way to manage this situation is to break the custom
      configuration changes for your site into three files.  You could add
      this to the end of your <filename>postgresql.conf</> file to include
      them:
<programlisting>
include 'shared.conf'
include 'memory.conf'
include 'server.conf'
</programlisting>
      All systems would have the same <filename>shared.conf</>.  Each
      server with a particular amount of memory could share the
      same <filename>memory.conf</>; you might have one for all servers
      with 8GB of RAM, another for those having 16GB.  And
      finally <filename>server.conf</> could have truly server-specific
      configuration information in it.
     </para>

     <para>
      Another possibility is to create a configuration file directory and
      put this information into files there. For example, a <filename>conf.d</>
      directory could be referenced at the end of <filename>postgresql.conf</>:
<programlisting>
include_dir 'conf.d'
</programlisting>
      Then you could name the files in the <filename>conf.d</> directory
      like this:
<programlisting>
00shared.conf
01memory.conf
02server.conf
</programlisting>
       This naming convention establishes a clear order in which these
       files will be loaded.  This is important because only the last
       setting encountered for a particular parameter while the server is
       reading configuration files will be used.  In this example,
       something set in <filename>conf.d/02server.conf</> would override a
       value set in <filename>conf.d/01memory.conf</>.
     </para>

     <para>
      You might instead use this approach to naming the files
      descriptively:
<programlisting>
00shared.conf
01memory-8GB.conf
02server-foo.conf
</programlisting>
      This sort of arrangement gives a unique name for each configuration file
      variation.  This can help eliminate ambiguity when several servers have
      their configurations all stored in one place, such as in a version
      control repository.  (Storing database configuration files under version
      control is another good practice to consider.)
     </para>
    </sect2>
   </sect1>

   <sect1 id="runtime-config-file-locations">
    <title>File Locations</title>

     <para>
      In addition to the <filename>postgresql.conf</filename> file
      already mentioned, <productname>PostgreSQL</productname> uses
      two other manually-edited configuration files, which control
      client authentication (their use is discussed in <xref
      linkend="client-authentication">).  By default, all three
      configuration files are stored in the database cluster's data
      directory.  The parameters described in this section allow the
      configuration files to be placed elsewhere.  (Doing so can ease
      administration.  In particular it is often easier to ensure that
      the configuration files are properly backed-up when they are
      kept separate.)
     </para>

     <variablelist>
     <varlistentry id="guc-data-directory" xreflabel="data_directory">
      <term><varname>data_directory</varname> (<type>string</type>)
      <indexterm>
       <primary><varname>data_directory</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
         Specifies the directory to use for data storage.
         This parameter can only be set at server start.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-config-file" xreflabel="config_file">
      <term><varname>config_file</varname> (<type>string</type>)
      <indexterm>
       <primary><varname>config_file</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
         Specifies the main server configuration file
         (customarily called <filename>postgresql.conf</>).
         This parameter can only be set on the <command>postgres</command> command line.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-hba-file" xreflabel="hba_file">
      <term><varname>hba_file</varname> (<type>string</type>)
      <indexterm>
       <primary><varname>hba_file</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
         Specifies the configuration file for host-based authentication
         (customarily called <filename>pg_hba.conf</>).
         This parameter can only be set at server start.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-ident-file" xreflabel="ident_file">
      <term><varname>ident_file</varname> (<type>string</type>)
      <indexterm>
       <primary><varname>ident_file</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
         Specifies the configuration file for user name mapping
         (customarily called <filename>pg_ident.conf</>).
         This parameter can only be set at server start.
         See also <xref linkend="auth-username-maps">.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-external-pid-file" xreflabel="external_pid_file">
      <term><varname>external_pid_file</varname> (<type>string</type>)
      <indexterm>
       <primary><varname>external_pid_file</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Specifies the name of an additional process-ID (PID) file that the
        server should create for use by server administration programs.
        This parameter can only be set at server start.
       </para>
      </listitem>
     </varlistentry>
     </variablelist>

     <para>
      In a default installation, none of the above parameters are set
      explicitly.  Instead, the
      data directory is specified by the <option>-D</option> command-line
      option or the <envar>PGDATA</envar> environment variable, and the
      configuration files are all found within the data directory.
     </para>

     <para>
      If you wish to keep the configuration files elsewhere than the
      data directory, the <command>postgres</command> <option>-D</option>
      command-line option or <envar>PGDATA</envar> environment variable
      must point to the directory containing the configuration files,
      and the <varname>data_directory</> parameter must be set in
      <filename>postgresql.conf</filename> (or on the command line) to show
      where the data directory is actually located.  Notice that
      <varname>data_directory</> overrides <option>-D</option> and
      <envar>PGDATA</envar> for the location
      of the data directory, but not for the location of the configuration
      files.
     </para>

     <para>
      If you wish, you can specify the configuration file names and locations
      individually using the parameters <varname>config_file</>,
      <varname>hba_file</> and/or <varname>ident_file</>.
      <varname>config_file</> can only be specified on the
      <command>postgres</command> command line, but the others can be
      set within the main configuration file.  If all three parameters plus
      <varname>data_directory</> are explicitly set, then it is not necessary
      to specify <option>-D</option> or <envar>PGDATA</envar>.
     </para>

     <para>
      When setting any of these parameters, a relative path will be interpreted
      with respect to the directory in which <command>postgres</command>
      is started.
     </para>
   </sect1>

   <sect1 id="runtime-config-connection">
    <title>Connections and Authentication</title>

    <sect2 id="runtime-config-connection-settings">
     <title>Connection Settings</title>

     <variablelist>

     <varlistentry id="guc-listen-addresses" xreflabel="listen_addresses">
      <term><varname>listen_addresses</varname> (<type>string</type>)
      <indexterm>
       <primary><varname>listen_addresses</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
         Specifies the TCP/IP address(es) on which the server is
         to listen for connections from client applications.
         The value takes the form of a comma-separated list of host names
         and/or numeric IP addresses.  The special entry <literal>*</>
         corresponds to all available IP interfaces.  The entry
         <literal>0.0.0.0</> allows listening for all IPv4 addresses and
         <literal>::</> allows listening for all IPv6 addresses.
         If the list is empty, the server does not listen on any IP interface
         at all, in which case only Unix-domain sockets can be used to connect
         to it.
         The default value is <systemitem class="systemname">localhost</>,
         which allows only local TCP/IP <quote>loopback</> connections to be
         made.  While client authentication (<xref
         linkend="client-authentication">) allows fine-grained control
         over who can access the server, <varname>listen_addresses</varname>
         controls which interfaces accept connection attempts, which
         can help prevent repeated malicious connection requests on
         insecure network interfaces.  This parameter can only be set
         at server start.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-port" xreflabel="port">
      <term><varname>port</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>port</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        The TCP port the server listens on; 5432 by default.  Note that the
        same port number is used for all IP addresses the server listens on.
        This parameter can only be set at server start.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-max-connections" xreflabel="max_connections">
      <term><varname>max_connections</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>max_connections</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Determines the maximum number of concurrent connections to the
        database server. The default is typically 100 connections, but
        might be less if your kernel settings will not support it (as
        determined during <application>initdb</>).  This parameter can
        only be set at server start.
       </para>

       <para>
        When running a standby server, you must set this parameter to the
        same or higher value than on the master server. Otherwise, queries
        will not be allowed in the standby server.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-superuser-reserved-connections"
     xreflabel="superuser_reserved_connections">
      <term><varname>superuser_reserved_connections</varname>
      (<type>integer</type>)
      <indexterm>
       <primary><varname>superuser_reserved_connections</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Determines the number of connection <quote>slots</quote> that
        are reserved for connections by <productname>PostgreSQL</>
        superusers.  At most <xref linkend="guc-max-connections">
        connections can ever be active simultaneously.  Whenever the
        number of active concurrent connections is at least
        <varname>max_connections</> minus
        <varname>superuser_reserved_connections</varname>, new
        connections will be accepted only for superusers, and no
        new replication connections will be accepted.
       </para>

       <para>
        The default value is three connections. The value must be less
        than the value of <varname>max_connections</varname>. This
        parameter can only be set at server start.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-unix-socket-directories" xreflabel="unix_socket_directories">
      <term><varname>unix_socket_directories</varname> (<type>string</type>)
      <indexterm>
       <primary><varname>unix_socket_directories</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Specifies the directory of the Unix-domain socket(s) on which the
        server is to listen for connections from client applications.
        Multiple sockets can be created by listing multiple directories
        separated by commas.  Whitespace between entries is
        ignored; surround a directory name with double quotes if you need
        to include whitespace or commas in the name.
        An empty value
        specifies not listening on any Unix-domain sockets, in which case
        only TCP/IP sockets can be used to connect to the server.
        The default value is normally
        <filename>/tmp</filename>, but that can be changed at build time.
        This parameter can only be set at server start.
       </para>

       <para>
        In addition to the socket file itself, which is named
        <literal>.s.PGSQL.<replaceable>nnnn</></literal> where
        <replaceable>nnnn</> is the server's port number, an ordinary file
        named <literal>.s.PGSQL.<replaceable>nnnn</>.lock</literal> will be
        created in each of the <varname>unix_socket_directories</> directories.
        Neither file should ever be removed manually.
       </para>

       <para>
        This parameter is irrelevant on Windows, which does not have
        Unix-domain sockets.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-unix-socket-group" xreflabel="unix_socket_group">
      <term><varname>unix_socket_group</varname> (<type>string</type>)
      <indexterm>
       <primary><varname>unix_socket_group</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Sets the owning group of the Unix-domain socket(s).  (The owning
        user of the sockets is always the user that starts the
        server.)  In combination with the parameter
        <varname>unix_socket_permissions</varname> this can be used as
        an additional access control mechanism for Unix-domain connections.
        By default this is the empty string, which uses the default
        group of the server user.  This parameter can only be set at
        server start.
       </para>

       <para>
        This parameter is irrelevant on Windows, which does not have
        Unix-domain sockets.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-unix-socket-permissions" xreflabel="unix_socket_permissions">
      <term><varname>unix_socket_permissions</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>unix_socket_permissions</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Sets the access permissions of the Unix-domain socket(s).  Unix-domain
        sockets use the usual Unix file system permission set.
        The parameter value is expected to be a numeric mode
        specified in the format accepted by the
        <function>chmod</function> and <function>umask</function>
        system calls.  (To use the customary octal format the number
        must start with a <literal>0</literal> (zero).)
       </para>

       <para>
        The default permissions are <literal>0777</literal>, meaning
        anyone can connect. Reasonable alternatives are
        <literal>0770</literal> (only user and group, see also
        <varname>unix_socket_group</varname>) and <literal>0700</literal>
        (only user). (Note that for a Unix-domain socket, only write
        permission matters, so there is no point in setting or revoking
        read or execute permissions.)
       </para>

       <para>
        This access control mechanism is independent of the one
        described in <xref linkend="client-authentication">.
       </para>

       <para>
        This parameter can only be set at server start.
       </para>

       <para>
        This parameter is irrelevant on systems, notably Solaris as of Solaris
        10, that ignore socket permissions entirely.  There, one can achieve a
        similar effect by pointing <varname>unix_socket_directories</> to a
        directory having search permission limited to the desired audience.
        This parameter is also irrelevant on Windows, which does not have
        Unix-domain sockets.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-bonjour" xreflabel="bonjour">
      <term><varname>bonjour</varname> (<type>boolean</type>)
      <indexterm>
       <primary><varname>bonjour</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Enables advertising the server's existence via
        <productname>Bonjour</productname>.  The default is off.
        This parameter can only be set at server start.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-bonjour-name" xreflabel="bonjour_name">
      <term><varname>bonjour_name</varname> (<type>string</type>)
      <indexterm>
       <primary><varname>bonjour_name</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Specifies the <productname>Bonjour</productname> service
        name.  The computer name is used if this parameter is set to the
        empty string <literal>''</> (which is the default).  This parameter is
        ignored if the server was not compiled with
        <productname>Bonjour</productname> support.
        This parameter can only be set at server start.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-tcp-keepalives-idle" xreflabel="tcp_keepalives_idle">
      <term><varname>tcp_keepalives_idle</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>tcp_keepalives_idle</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Specifies the number of seconds of inactivity after which TCP
        should send a keepalive message to the client.  A value of 0 uses
        the system default.
        This parameter is supported only on systems that support
        <symbol>TCP_KEEPIDLE</> or an equivalent socket option, and on
        Windows; on other systems, it must be zero.
        In sessions connected via a Unix-domain socket, this parameter is
        ignored and always reads as zero.
       </para>
       <note>
        <para>
         On Windows, a value of 0 will set this parameter to 2 hours,
         since Windows does not provide a way to read the system default value.
        </para>
       </note>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-tcp-keepalives-interval" xreflabel="tcp_keepalives_interval">
      <term><varname>tcp_keepalives_interval</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>tcp_keepalives_interval</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Specifies the number of seconds after which a TCP keepalive message
        that is not acknowledged by the client should be retransmitted.
        A value of 0 uses the system default.
        This parameter is supported only on systems that support
        <symbol>TCP_KEEPINTVL</> or an equivalent socket option, and on
        Windows; on other systems, it must be zero.
        In sessions connected via a Unix-domain socket, this parameter is
        ignored and always reads as zero.
       </para>
       <note>
        <para>
         On Windows, a value of 0 will set this parameter to 1 second,
         since Windows does not provide a way to read the system default value.
        </para>
       </note>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-tcp-keepalives-count" xreflabel="tcp_keepalives_count">
      <term><varname>tcp_keepalives_count</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>tcp_keepalives_count</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Specifies the number of TCP keepalives that can be lost before
        the server's connection to the client is considered dead.
        A value of 0 uses the system default.
        This parameter is supported only on systems that support
        <symbol>TCP_KEEPCNT</> or an equivalent socket option;
        on other systems, it must be zero.
        In sessions connected via a Unix-domain socket, this parameter is
        ignored and always reads as zero.
       </para>
       <note>
        <para>
         This parameter is not supported on Windows, and must be zero.
        </para>
       </note>
      </listitem>
     </varlistentry>

     </variablelist>
     </sect2>
     <sect2 id="runtime-config-connection-security">
     <title>Security and Authentication</title>

     <variablelist>
     <varlistentry id="guc-authentication-timeout" xreflabel="authentication_timeout">
      <term><varname>authentication_timeout</varname> (<type>integer</type>)
      <indexterm><primary>timeout</><secondary>client authentication</></indexterm>
      <indexterm><primary>client authentication</><secondary>timeout during</></indexterm>
      <indexterm>
       <primary><varname>authentication_timeout</> configuration parameter</primary>
      </indexterm>
      </term>

      <listitem>
       <para>
        Maximum time to complete client authentication, in seconds. If a
        would-be client has not completed the authentication protocol in
        this much time, the server closes the connection. This prevents
        hung clients from occupying a connection indefinitely.
        The default is one minute (<literal>1m</>).
        This parameter can only be set in the <filename>postgresql.conf</>
        file or on the server command line.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-ssl" xreflabel="ssl">
      <term><varname>ssl</varname> (<type>boolean</type>)
      <indexterm>
       <primary><varname>ssl</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Enables <acronym>SSL</> connections. Please read
        <xref linkend="ssl-tcp"> before using this. The default
        is <literal>off</>. This parameter can only be set at server
        start.  <acronym>SSL</> communication is only possible with
        TCP/IP connections.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-ssl-ca-file" xreflabel="ssl_ca_file">
      <term><varname>ssl_ca_file</varname> (<type>string</type>)
      <indexterm>
       <primary><varname>ssl_ca_file</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Specifies the name of the file containing the SSL server certificate
        authority (CA).  The default is empty, meaning no CA file is loaded,
        and client certificate verification is not performed.  (In previous
        releases of PostgreSQL, the name of this file was hard-coded
        as <filename>root.crt</filename>.)  Relative paths are relative to the
        data directory.  This parameter can only be set at server start.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-ssl-cert-file" xreflabel="ssl_cert_file">
      <term><varname>ssl_cert_file</varname> (<type>string</type>)
      <indexterm>
       <primary><varname>ssl_cert_file</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Specifies the name of the file containing the SSL server certificate.
        The default is <filename>server.crt</filename>.  Relative paths are
        relative to the data directory.  This parameter can only be set at
        server start.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-ssl-crl-file" xreflabel="ssl_crl_file">
      <term><varname>ssl_crl_file</varname> (<type>string</type>)
      <indexterm>
       <primary><varname>ssl_crl_file</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Specifies the name of the file containing the SSL server certificate
        revocation list (CRL).  The default is empty, meaning no CRL file is
        loaded.  (In previous releases of PostgreSQL, the name of this file was
        hard-coded as <filename>root.crl</filename>.)  Relative paths are
        relative to the data directory.  This parameter can only be set at
        server start.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-ssl-key-file" xreflabel="ssl_key_file">
      <term><varname>ssl_key_file</varname> (<type>string</type>)
      <indexterm>
       <primary><varname>ssl_key_file</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Specifies the name of the file containing the SSL server private key.
        The default is <filename>server.key</filename>.  Relative paths are
        relative to the data directory.  This parameter can only be set at
        server start.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-ssl-ciphers" xreflabel="ssl_ciphers">
      <term><varname>ssl_ciphers</varname> (<type>string</type>)
      <indexterm>
       <primary><varname>ssl_ciphers</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Specifies a list of <acronym>SSL</> cipher suites that are allowed to be
        used on secure connections.  See
        the <citerefentry><refentrytitle>ciphers</></citerefentry> manual page
        in the <application>OpenSSL</> package for the syntax of this setting
        and a list of supported values.  The default value is
        <literal>HIGH:MEDIUM:+3DES:!aNULL</>.  It is usually reasonable,
        unless you have specific security requirements.  This parameter can only
        be set at server start.
       </para>

       <para>
        Explanation of the default value:
        <variablelist>
         <varlistentry>
          <term><literal>HIGH</literal></term>
          <listitem>
           <para>
            Cipher suites that use ciphers from <literal>HIGH</> group (e.g.,
            AES, Camellia, 3DES)
           </para>
          </listitem>
         </varlistentry>

         <varlistentry>
          <term><literal>MEDIUM</literal></term>
          <listitem>
           <para>
            Cipher suites that use ciphers from <literal>MEDIUM</> group
            (e.g., RC4, SEED)
           </para>
          </listitem>
         </varlistentry>

         <varlistentry>
          <term><literal>+3DES</literal></term>
          <listitem>
           <para>
            The OpenSSL default order for <literal>HIGH</> is problematic
            because it orders 3DES higher than AES128.  This is wrong because
            3DES offers less security than AES128, and it is also much
            slower.  <literal>+3DES</> reorders it after all other
            <literal>HIGH</> and <literal>MEDIUM</> ciphers.
           </para>
          </listitem>
         </varlistentry>

         <varlistentry>
          <term><literal>!aNULL</literal></term>
          <listitem>
           <para>
            Disables anonymous cipher suites that do no authentication.  Such
            cipher suites are vulnerable to man-in-the-middle attacks and
            therefore should not be used.
           </para>
          </listitem>
         </varlistentry>
        </variablelist>
       </para>

       <para>
        Available cipher suite details will vary across OpenSSL versions.  Use
        the command
        <literal>openssl ciphers -v 'HIGH:MEDIUM:+3DES:!aNULL'</literal> to
        see actual details for the currently installed <application>OpenSSL</>
        version.  Note that this list is filtered at run time based on the
        server key type.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-ssl-prefer-server-ciphers" xreflabel="ssl_prefer_server_ciphers">
      <term><varname>ssl_prefer_server_ciphers</varname> (<type>bool</type>)
      <indexterm>
       <primary><varname>ssl_prefer_server_ciphers</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Specifies whether to use the server's SSL cipher preferences, rather
        than the client's.  The default is true.  This parameter can only be
        set at server start.
       </para>

       <para>
        Older PostgreSQL versions do not have this setting and always use the
        client's preferences.  This setting is mainly for backward
        compatibility with those versions.  Using the server's preferences is
        usually better because it is more likely that the server is appropriately
        configured.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-ssl-ecdh-curve" xreflabel="ssl_ecdh_curve">
      <term><varname>ssl_ecdh_curve</varname> (<type>string</type>)
      <indexterm>
       <primary><varname>ssl_ecdh_curve</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Specifies the name of the curve to use in <acronym>ECDH</> key
        exchange.  It needs to be supported by all clients that connect.
        It does not need to be same curve as used by server's Elliptic
        Curve key.  The default is <literal>prime256v1</>.  This parameter
        can only be set at server start.
       </para>

       <para>
        OpenSSL names for most common curves:
        <literal>prime256v1</> (NIST P-256),
        <literal>secp384r1</> (NIST P-384),
        <literal>secp521r1</> (NIST P-521).
       </para>

       <para>
        The full list of available curves can be shown with the command
        <command>openssl ecparam -list_curves</command>.  Not all of them
        are usable in <acronym>TLS</> though.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-password-encryption" xreflabel="password_encryption">
      <term><varname>password_encryption</varname> (<type>boolean</type>)
      <indexterm>
       <primary><varname>password_encryption</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        When a password is specified in <xref
        linkend="sql-createuser"> or
        <xref linkend="sql-alterrole">
        without writing either <literal>ENCRYPTED</> or
        <literal>UNENCRYPTED</>, this parameter determines whether the
        password is to be encrypted. The default is <literal>on</>
        (encrypt the password).
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-krb-server-keyfile" xreflabel="krb_server_keyfile">
      <term><varname>krb_server_keyfile</varname> (<type>string</type>)
      <indexterm>
       <primary><varname>krb_server_keyfile</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Sets the location of the Kerberos server key file. See
        <xref linkend="gssapi-auth">
        for details. This parameter can only be set in the
        <filename>postgresql.conf</> file or on the server command line.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-krb-caseins-users" xreflabel="krb_caseins_users">
      <term><varname>krb_caseins_users</varname> (<type>boolean</type>)
      <indexterm>
       <primary><varname>krb_caseins_users</varname> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Sets whether GSSAPI user names should be treated
        case-insensitively.
        The default is <literal>off</> (case sensitive). This parameter can only be
        set in the <filename>postgresql.conf</> file or on the server command line.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-db-user-namespace" xreflabel="db_user_namespace">
      <term><varname>db_user_namespace</varname> (<type>boolean</type>)
      <indexterm>
       <primary><varname>db_user_namespace</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        This parameter enables per-database user names.  It is off by default.
        This parameter can only be set in the <filename>postgresql.conf</>
        file or on the server command line.
       </para>

       <para>
        If this is on, you should create users as <replaceable>username@dbname</>.
        When <replaceable>username</> is passed by a connecting client,
        <literal>@</> and the database name are appended to the user
        name and that database-specific user name is looked up by the
        server. Note that when you create users with names containing
        <literal>@</> within the SQL environment, you will need to
        quote the user name.
       </para>

       <para>
        With this parameter enabled, you can still create ordinary global
        users.  Simply append <literal>@</> when specifying the user
        name in the client, e.g. <literal>joe@</>.  The <literal>@</>
        will be stripped off before the user name is looked up by the
        server.
       </para>

       <para>
        <varname>db_user_namespace</> causes the client's and
        server's user name representation to differ.
        Authentication checks are always done with the server's user name
        so authentication methods must be configured for the
        server's user name, not the client's.  Because
        <literal>md5</> uses the user name as salt on both the
        client and server, <literal>md5</> cannot be used with
        <varname>db_user_namespace</>.
       </para>

       <note>
        <para>
         This feature is intended as a temporary measure until a
         complete solution is found.  At that time, this option will
         be removed.
        </para>
       </note>
      </listitem>
     </varlistentry>

    </variablelist>
    </sect2>
   </sect1>

   <sect1 id="runtime-config-resource">
    <title>Resource Consumption</title>

    <sect2 id="runtime-config-resource-memory">
     <title>Memory</title>

     <variablelist>
     <varlistentry id="guc-shared-buffers" xreflabel="shared_buffers">
      <term><varname>shared_buffers</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>shared_buffers</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Sets the amount of memory the database server uses for shared
        memory buffers.  The default is typically 128 megabytes
        (<literal>128MB</>), but might be less if your kernel settings will
        not support it (as determined during <application>initdb</>).
        This setting must be at least 128 kilobytes.  (Non-default
        values of <symbol>BLCKSZ</symbol> change the minimum.)  However,
        settings significantly higher than the minimum are usually needed
        for good performance.  This parameter can only be set at server start.
       </para>

       <para>
        If you have a dedicated database server with 1GB or more of RAM, a
        reasonable starting value for <varname>shared_buffers</varname> is 25%
        of the memory in your system.  There are some workloads where even
        large settings for <varname>shared_buffers</varname> are effective, but
        because <productname>PostgreSQL</productname> also relies on the
        operating system cache, it is unlikely that an allocation of more than
        40% of RAM to <varname>shared_buffers</varname> will work better than a
        smaller amount.  Larger settings for <varname>shared_buffers</varname>
        usually require a corresponding increase in
        <varname>max_wal_size</varname>, in order to spread out the
        process of writing large quantities of new or changed data over a
        longer period of time.
       </para>

       <para>
        On systems with less than 1GB of RAM, a smaller percentage of RAM is
        appropriate, so as to leave adequate space for the operating system.
        Also, on Windows, large values for <varname>shared_buffers</varname>
        aren't as effective.  You may find better results keeping the setting
        relatively low and using the operating system cache more instead.  The
        useful range for <varname>shared_buffers</varname> on Windows systems
        is generally from 64MB to 512MB.
       </para>

      </listitem>
     </varlistentry>

     <varlistentry id="guc-huge-pages" xreflabel="huge_pages">
      <term><varname>huge_pages</varname> (<type>enum</type>)
      <indexterm>
       <primary><varname>huge_pages</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Enables/disables the use of huge memory pages. Valid values are
        <literal>try</literal> (the default), <literal>on</literal>,
        and <literal>off</literal>.
       </para>

       <para>
        At present, this feature is supported only on Linux. The setting is
        ignored on other systems when set to <literal>try</literal>.
       </para>

       <para>
        The use of huge pages results in smaller page tables and less CPU time
        spent on memory management, increasing performance. For more details,
        see <xref linkend="linux-huge-pages">.
       </para>

       <para>
        With <varname>huge_pages</varname> set to <literal>try</literal>,
        the server will try to use huge pages, but fall back to using
        normal allocation if that fails. With <literal>on</literal>, failure
        to use huge pages will prevent the server from starting up. With
        <literal>off</literal>, huge pages will not be used.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-temp-buffers" xreflabel="temp_buffers">
      <term><varname>temp_buffers</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>temp_buffers</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Sets the maximum number of temporary buffers used by each database
        session.  These are session-local buffers used only for access to
        temporary tables.  The default is eight megabytes
        (<literal>8MB</>).  The setting can be changed within individual
        sessions, but only before the first use of temporary tables
        within the session; subsequent attempts to change the value will
        have no effect on that session.
       </para>

       <para>
        A session will allocate temporary buffers as needed up to the limit
        given by <varname>temp_buffers</>.  The cost of setting a large
        value in sessions that do not actually need many temporary
        buffers is only a buffer descriptor, or about 64 bytes, per
        increment in <varname>temp_buffers</>.  However if a buffer is
        actually used an additional 8192 bytes will be consumed for it
        (or in general, <symbol>BLCKSZ</symbol> bytes).
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-max-prepared-transactions" xreflabel="max_prepared_transactions">
      <term><varname>max_prepared_transactions</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>max_prepared_transactions</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Sets the maximum number of transactions that can be in the
        <quote>prepared</> state simultaneously (see <xref
        linkend="sql-prepare-transaction">).
        Setting this parameter to zero (which is the default)
        disables the prepared-transaction feature.
        This parameter can only be set at server start.
       </para>

       <para>
        If you are not planning to use prepared transactions, this parameter
        should be set to zero to prevent accidental creation of prepared
        transactions.  If you are using prepared transactions, you will
        probably want <varname>max_prepared_transactions</varname> to be at
        least as large as <xref linkend="guc-max-connections">, so that every
        session can have a prepared transaction pending.
       </para>

       <para>
        When running a standby server, you must set this parameter to the
        same or higher value than on the master server. Otherwise, queries
        will not be allowed in the standby server.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-work-mem" xreflabel="work_mem">
      <term><varname>work_mem</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>work_mem</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Specifies the amount of memory to be used by internal sort operations
        and hash tables before writing to temporary disk files. The value
        defaults to four megabytes (<literal>4MB</>).
        Note that for a complex query, several sort or hash operations might be
        running in parallel; each operation will be allowed to use as much memory
        as this value specifies before it starts to write data into temporary
        files. Also, several running sessions could be doing such operations
        concurrently.  Therefore, the total memory used could be many
        times the value of <varname>work_mem</varname>; it is necessary to
        keep this fact in mind when choosing the value. Sort operations are
        used for <literal>ORDER BY</>, <literal>DISTINCT</>, and
        merge joins.
        Hash tables are used in hash joins, hash-based aggregation, and
        hash-based processing of <literal>IN</> subqueries.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-maintenance-work-mem" xreflabel="maintenance_work_mem">
      <term><varname>maintenance_work_mem</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>maintenance_work_mem</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Specifies the maximum amount of memory to be used by maintenance
        operations, such as <command>VACUUM</command>, <command>CREATE
        INDEX</>, and <command>ALTER TABLE ADD FOREIGN KEY</>.  It defaults
        to 64 megabytes (<literal>64MB</>).  Since only one of these
        operations can be executed at a time by a database session, and
        an installation normally doesn't have many of them running
        concurrently, it's safe to set this value significantly larger
        than <varname>work_mem</varname>.  Larger settings might improve
        performance for vacuuming and for restoring database dumps.
       </para>
       <para>
        Note that when autovacuum runs, up to
        <xref linkend="guc-autovacuum-max-workers"> times this memory
        may be allocated, so be careful not to set the default value
        too high.  It may be useful to control for this by separately
        setting <xref linkend="guc-autovacuum-work-mem">.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-replacement-sort-tuples" xreflabel="replacement_sort_tuples">
      <term><varname>replacement_sort_tuples</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>replacement_sort_tuples</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        When the number of tuples to be sorted is smaller than this number,
        a sort will produce its first output run using replacement selection
        rather than quicksort.  This may be useful in memory-constrained
        environments where tuples that are input into larger sort operations
        have a strong physical-to-logical correlation.  Note that this does
        not include input tuples with an <emphasis>inverse</emphasis>
        correlation.  It is possible for the replacement selection algorithm
        to generate one long run that requires no merging, where use of the
        default strategy would result in many runs that must be merged
        to produce a final sorted output.  This may allow sort
        operations to complete sooner.
       </para>
       <para>
        The default is 150,000 tuples.  Note that higher values are typically
        not much more effective, and may be counter-productive, since the
        priority queue is sensitive to the size of available CPU cache, whereas
        the default strategy sorts runs using a <firstterm>cache
        oblivious</firstterm> algorithm.  This property allows the default sort
        strategy to automatically and transparently make effective use
        of available CPU cache.
       </para>
       <para>
        Setting <varname>maintenance_work_mem</varname> to its default
        value usually prevents utility command external sorts (e.g.,
        sorts used by <command>CREATE INDEX</> to build B-Tree
        indexes) from ever using replacement selection sort, unless the
        input tuples are quite wide.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-autovacuum-work-mem" xreflabel="autovacuum_work_mem">
      <term><varname>autovacuum_work_mem</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>autovacuum_work_mem</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Specifies the maximum amount of memory to be used by each
        autovacuum worker process.  It defaults to -1, indicating that
        the value of <xref linkend="guc-maintenance-work-mem"> should
        be used instead.  The setting has no effect on the behavior of
        <command>VACUUM</command> when run in other contexts.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-max-stack-depth" xreflabel="max_stack_depth">
      <term><varname>max_stack_depth</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>max_stack_depth</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Specifies the maximum safe depth of the server's execution stack.
        The ideal setting for this parameter is the actual stack size limit
        enforced by the kernel (as set by <literal>ulimit -s</> or local
        equivalent), less a safety margin of a megabyte or so.  The safety
        margin is needed because the stack depth is not checked in every
        routine in the server, but only in key potentially-recursive routines
        such as expression evaluation.  The default setting is two
        megabytes (<literal>2MB</>), which is conservatively small and
        unlikely to risk crashes.  However, it might be too small to allow
        execution of complex functions.  Only superusers can change this
        setting.
       </para>

       <para>
        Setting <varname>max_stack_depth</> higher than
        the actual kernel limit will mean that a runaway recursive function
        can crash an individual backend process.  On platforms where
        <productname>PostgreSQL</productname> can determine the kernel limit,
        the server will not allow this variable to be set to an unsafe
        value.  However, not all platforms provide the information,
        so caution is recommended in selecting a value.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-dynamic-shared-memory-type" xreflabel="dynamic_shared_memory_type">
      <term><varname>dynamic_shared_memory_type</varname> (<type>enum</type>)
      <indexterm>
       <primary><varname>dynamic_shared_memory_type</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Specifies the dynamic shared memory implementation that the server
        should use.  Possible values are <literal>posix</> (for POSIX shared
        memory allocated using <literal>shm_open</>), <literal>sysv</literal>
        (for System V shared memory allocated via <literal>shmget</>),
        <literal>windows</> (for Windows shared memory), <literal>mmap</>
        (to simulate shared memory using memory-mapped files stored in the
        data directory), and <literal>none</> (to disable this feature).
        Not all values are supported on all platforms; the first supported
        option is the default for that platform.  The use of the
        <literal>mmap</> option, which is not the default on any platform,
        is generally discouraged because the operating system may write
        modified pages back to disk repeatedly, increasing system I/O load;
        however, it may be useful for debugging, when the
        <literal>pg_dynshmem</> directory is stored on a RAM disk, or when
        other shared memory facilities are not available.
       </para>
      </listitem>
     </varlistentry>

     </variablelist>
     </sect2>

     <sect2 id="runtime-config-resource-disk">
     <title>Disk</title>

     <variablelist>
     <varlistentry id="guc-temp-file-limit" xreflabel="temp_file_limit">
      <term><varname>temp_file_limit</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>temp_file_limit</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Specifies the maximum amount of disk space that a process can use
        for temporary files, such as sort and hash temporary files, or the
        storage file for a held cursor.  A transaction attempting to exceed
        this limit will be canceled.
        The value is specified in kilobytes, and <literal>-1</> (the
        default) means no limit.
        Only superusers can change this setting.
       </para>
       <para>
        This setting constrains the total space used at any instant by all
        temporary files used by a given <productname>PostgreSQL</> process.
        It should be noted that disk space used for explicit temporary
        tables, as opposed to temporary files used behind-the-scenes in query
        execution, does <emphasis>not</emphasis> count against this limit.
       </para>
      </listitem>
     </varlistentry>

     </variablelist>
     </sect2>

     <sect2 id="runtime-config-resource-kernel">
     <title>Kernel Resource Usage</title>

     <variablelist>
     <varlistentry id="guc-max-files-per-process" xreflabel="max_files_per_process">
      <term><varname>max_files_per_process</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>max_files_per_process</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Sets the maximum number of simultaneously open files allowed to each
        server subprocess. The default is one thousand files. If the kernel is enforcing
        a safe per-process limit, you don't need to worry about this setting.
        But on some platforms (notably, most BSD systems), the kernel will
        allow individual processes to open many more files than the system
        can actually support if many processes all try to open
        that many files. If you find yourself seeing <quote>Too many open
        files</> failures, try reducing this setting.
        This parameter can only be set at server start.
       </para>
      </listitem>
     </varlistentry>
     </variablelist>
    </sect2>

    <sect2 id="runtime-config-resource-vacuum-cost">
     <title>Cost-based Vacuum Delay</title>

     <para>
      During the execution of <xref linkend="sql-vacuum">
      and <xref linkend="sql-analyze">
      commands, the system maintains an
      internal counter that keeps track of the estimated cost of the
      various I/O operations that are performed.  When the accumulated
      cost reaches a limit (specified by
      <varname>vacuum_cost_limit</varname>), the process performing
      the operation will sleep for a short period of time, as specified by
      <varname>vacuum_cost_delay</varname>. Then it will reset the
      counter and continue execution.
     </para>

     <para>
      The intent of this feature is to allow administrators to reduce
      the I/O impact of these commands on concurrent database
      activity. There are many situations where it is not
      important that maintenance commands like
      <command>VACUUM</command> and <command>ANALYZE</command> finish
      quickly; however, it is usually very important that these
      commands do not significantly interfere with the ability of the
      system to perform other database operations. Cost-based vacuum
      delay provides a way for administrators to achieve this.
     </para>

     <para>
      This feature is disabled by default for manually issued
      <command>VACUUM</command> commands. To enable it, set the
      <varname>vacuum_cost_delay</varname> variable to a nonzero
      value.
     </para>

     <variablelist>
      <varlistentry id="guc-vacuum-cost-delay" xreflabel="vacuum_cost_delay">
       <term><varname>vacuum_cost_delay</varname> (<type>integer</type>)
       <indexterm>
        <primary><varname>vacuum_cost_delay</> configuration parameter</primary>
       </indexterm>
       </term>
       <listitem>
        <para>
         The length of time, in milliseconds, that the process will sleep
         when the cost limit has been exceeded.
         The default value is zero, which disables the cost-based vacuum
         delay feature.  Positive values enable cost-based vacuuming.
         Note that on many systems, the effective resolution
         of sleep delays is 10 milliseconds; setting
         <varname>vacuum_cost_delay</varname> to a value that is
         not a multiple of 10 might have the same results as setting it
         to the next higher multiple of 10.
        </para>

        <para>
         When using cost-based vacuuming, appropriate values for
         <varname>vacuum_cost_delay</> are usually quite small, perhaps
         10 or 20 milliseconds.  Adjusting vacuum's resource consumption
         is best done by changing the other vacuum cost parameters.
        </para>
       </listitem>
      </varlistentry>

      <varlistentry id="guc-vacuum-cost-page-hit" xreflabel="vacuum_cost_page_hit">
       <term><varname>vacuum_cost_page_hit</varname> (<type>integer</type>)
       <indexterm>
        <primary><varname>vacuum_cost_page_hit</> configuration parameter</primary>
       </indexterm>
       </term>
       <listitem>
        <para>
         The estimated cost for vacuuming a buffer found in the shared buffer
         cache. It represents the cost to lock the buffer pool, lookup
         the shared hash table and scan the content of the page. The
         default value is one.
        </para>
       </listitem>
      </varlistentry>

      <varlistentry id="guc-vacuum-cost-page-miss" xreflabel="vacuum_cost_page_miss">
       <term><varname>vacuum_cost_page_miss</varname> (<type>integer</type>)
       <indexterm>
        <primary><varname>vacuum_cost_page_miss</> configuration parameter</primary>
       </indexterm>
       </term>
       <listitem>
        <para>
         The estimated cost for vacuuming a buffer that has to be read from
         disk.  This represents the effort to lock the buffer pool,
         lookup the shared hash table, read the desired block in from
         the disk and scan its content. The default value is 10.
        </para>
       </listitem>
      </varlistentry>

      <varlistentry id="guc-vacuum-cost-page-dirty" xreflabel="vacuum_cost_page_dirty">
       <term><varname>vacuum_cost_page_dirty</varname> (<type>integer</type>)
       <indexterm>
        <primary><varname>vacuum_cost_page_dirty</> configuration parameter</primary>
       </indexterm>
       </term>
       <listitem>
        <para>
         The estimated cost charged when vacuum modifies a block that was
         previously clean. It represents the extra I/O required to
         flush the dirty block out to disk again. The default value is
         20.
        </para>
       </listitem>
      </varlistentry>

      <varlistentry id="guc-vacuum-cost-limit" xreflabel="vacuum_cost_limit">
       <term><varname>vacuum_cost_limit</varname> (<type>integer</type>)
       <indexterm>
        <primary><varname>vacuum_cost_limit</> configuration parameter</primary>
       </indexterm>
       </term>
       <listitem>
        <para>
         The accumulated cost that will cause the vacuuming process to sleep.
         The default value is 200.
        </para>
       </listitem>
      </varlistentry>
     </variablelist>

     <note>
      <para>
       There are certain operations that hold critical locks and should
       therefore complete as quickly as possible.  Cost-based vacuum
       delays do not occur during such operations.  Therefore it is
       possible that the cost accumulates far higher than the specified
       limit.  To avoid uselessly long delays in such cases, the actual
       delay is calculated as <varname>vacuum_cost_delay</varname> *
       <varname>accumulated_balance</varname> /
       <varname>vacuum_cost_limit</varname> with a maximum of
       <varname>vacuum_cost_delay</varname> * 4.
      </para>
     </note>
    </sect2>

    <sect2 id="runtime-config-resource-background-writer">
     <title>Background Writer</title>

     <para>
      There is a separate server
      process called the <firstterm>background writer</>, whose function
      is to issue writes of <quote>dirty</> (new or modified) shared
      buffers.  It writes shared buffers so server processes handling
      user queries seldom or never need to wait for a write to occur.
      However, the background writer does cause a net overall
      increase in I/O load, because while a repeatedly-dirtied page might
      otherwise be written only once per checkpoint interval, the
      background writer might write it several times as it is dirtied
      in the same interval.  The parameters discussed in this subsection
      can be used to tune the behavior for local needs.
     </para>

     <variablelist>
      <varlistentry id="guc-bgwriter-delay" xreflabel="bgwriter_delay">
       <term><varname>bgwriter_delay</varname> (<type>integer</type>)
       <indexterm>
        <primary><varname>bgwriter_delay</> configuration parameter</primary>
       </indexterm>
       </term>
       <listitem>
        <para>
         Specifies the delay between activity rounds for the
         background writer.  In each round the writer issues writes
         for some number of dirty buffers (controllable by the
         following parameters).  It then sleeps for <varname>bgwriter_delay</>
         milliseconds, and repeats.  When there are no dirty buffers in the
         buffer pool, though, it goes into a longer sleep regardless of
         <varname>bgwriter_delay</>.  The default value is 200
         milliseconds (<literal>200ms</>). Note that on many systems, the
         effective resolution of sleep delays is 10 milliseconds; setting
         <varname>bgwriter_delay</> to a value that is not a multiple of 10
         might have the same results as setting it to the next higher multiple
         of 10.  This parameter can only be set in the
         <filename>postgresql.conf</> file or on the server command line.
        </para>
       </listitem>
      </varlistentry>

      <varlistentry id="guc-bgwriter-lru-maxpages" xreflabel="bgwriter_lru_maxpages">
       <term><varname>bgwriter_lru_maxpages</varname> (<type>integer</type>)
       <indexterm>
        <primary><varname>bgwriter_lru_maxpages</> configuration parameter</primary>
       </indexterm>
       </term>
       <listitem>
        <para>
         In each round, no more than this many buffers will be written
         by the background writer.  Setting this to zero disables
         background writing.  (Note that checkpoints, which are managed by
         a separate, dedicated auxiliary process, are unaffected.)
         The default value is 100 buffers.
         This parameter can only be set in the <filename>postgresql.conf</>
         file or on the server command line.
        </para>
       </listitem>
      </varlistentry>

      <varlistentry id="guc-bgwriter-lru-multiplier" xreflabel="bgwriter_lru_multiplier">
       <term><varname>bgwriter_lru_multiplier</varname> (<type>floating point</type>)
       <indexterm>
        <primary><varname>bgwriter_lru_multiplier</> configuration parameter</primary>
       </indexterm>
       </term>
       <listitem>
        <para>
         The number of dirty buffers written in each round is based on the
         number of new buffers that have been needed by server processes
         during recent rounds.  The average recent need is multiplied by
         <varname>bgwriter_lru_multiplier</> to arrive at an estimate of the
         number of buffers that will be needed during the next round.  Dirty
         buffers are written until there are that many clean, reusable buffers
         available.  (However, no more than <varname>bgwriter_lru_maxpages</>
         buffers will be written per round.)
         Thus, a setting of 1.0 represents a <quote>just in time</> policy
         of writing exactly the number of buffers predicted to be needed.
         Larger values provide some cushion against spikes in demand,
         while smaller values intentionally leave writes to be done by
         server processes.
         The default is 2.0.
         This parameter can only be set in the <filename>postgresql.conf</>
         file or on the server command line.
        </para>
       </listitem>
      </varlistentry>

      <varlistentry id="guc-bgwriter-flush-after" xreflabel="bgwriter_flush_after">
       <term><varname>bgwriter_flush_after</varname> (<type>integer</type>)
       <indexterm>
        <primary><varname>bgwriter_flush_after</> configuration parameter</primary>
       </indexterm>
       </term>
       <listitem>
        <para>
         Whenever more than <varname>bgwriter_flush_after</varname> bytes have
         been written by the bgwriter, attempt to force the OS to issue these
         writes to the underlying storage.  Doing so will limit the amount of
         dirty data in the kernel's page cache, reducing the likelihood of
         stalls when an fsync is issued at the end of a checkpoint, or when
         the OS writes data back in larger batches in the background.  Often
         that will result in greatly reduced transaction latency, but there
         also are some cases, especially with workloads that are bigger than
         <xref linkend="guc-shared-buffers">, but smaller than the OS's page
         cache, where performance might degrade.  This setting may have no
         effect on some platforms.  The valid range is between
         <literal>0</literal>, which disables forced writeback, and
         <literal>2MB</literal>.  The default is <literal>512kB</> on Linux,
         <literal>0</> elsewhere.  (If <symbol>BLCKSZ</symbol> is not 8kB,
         the default and maximum values scale proportionally to it.)
         This parameter can only be set in the <filename>postgresql.conf</>
         file or on the server command line.
        </para>
       </listitem>
      </varlistentry>
     </variablelist>

     <para>
      Smaller values of <varname>bgwriter_lru_maxpages</varname> and
      <varname>bgwriter_lru_multiplier</varname> reduce the extra I/O load
      caused by the background writer, but make it more likely that server
      processes will have to issue writes for themselves, delaying interactive
      queries.
     </para>
    </sect2>

    <sect2 id="runtime-config-resource-async-behavior">
     <title>Asynchronous Behavior</title>

     <variablelist>
      <varlistentry id="guc-effective-io-concurrency" xreflabel="effective_io_concurrency">
       <term><varname>effective_io_concurrency</varname> (<type>integer</type>)
       <indexterm>
        <primary><varname>effective_io_concurrency</> configuration parameter</primary>
       </indexterm>
       </term>
       <listitem>
        <para>
         Sets the number of concurrent disk I/O operations that
         <productname>PostgreSQL</> expects can be executed
         simultaneously.  Raising this value will increase the number of I/O
         operations that any individual <productname>PostgreSQL</> session
         attempts to initiate in parallel.  The allowed range is 1 to 1000,
         or zero to disable issuance of asynchronous I/O requests. Currently,
         this setting only affects bitmap heap scans.
        </para>

        <para>
         For magnetic drives, a good starting point for this setting is the
         number of separate
         drives comprising a RAID 0 stripe or RAID 1 mirror being used for the
         database.  (For RAID 5 the parity drive should not be counted.)
         However, if the database is often busy with multiple queries issued in
         concurrent sessions, lower values may be sufficient to keep the disk
         array busy.  A value higher than needed to keep the disks busy will
         only result in extra CPU overhead.
         SSDs and other memory-based storage can often process many
         concurrent requests, so the best value might be in the hundreds.
        </para>

        <para>
         Asynchronous I/O depends on an effective <function>posix_fadvise</>
         function, which some operating systems lack.  If the function is not
         present then setting this parameter to anything but zero will result
         in an error.  On some operating systems (e.g., Solaris), the function
         is present but does not actually do anything.
        </para>

        <para>
         The default is 1 on supported systems, otherwise 0.  This value can
         be overridden for tables in a particular tablespace by setting the
         tablespace parameter of the same name (see
         <xref linkend="sql-altertablespace">).
        </para>
       </listitem>
      </varlistentry>

      <varlistentry id="guc-max-worker-processes" xreflabel="max_worker_processes">
       <term><varname>max_worker_processes</varname> (<type>integer</type>)
       <indexterm>
        <primary><varname>max_worker_processes</> configuration parameter</primary>
       </indexterm>
       </term>
       <listitem>
        <para>
         Sets the maximum number of background processes that the system
         can support.  This parameter can only be set at server start.  The
         default is 8.
        </para>

        <para>
         When running a standby server, you must set this parameter to the
         same or higher value than on the master server. Otherwise, queries
         will not be allowed in the standby server.
        </para>
       </listitem>
      </varlistentry>

      <varlistentry id="guc-max-parallel-workers-per-gather" xreflabel="max_parallel_workers_per_gather">
       <term><varname>max_parallel_workers_per_gather</varname> (<type>integer</type>)
       <indexterm>
        <primary><varname>max_parallel_workers_per_gather</> configuration parameter</primary>
       </indexterm>
       </term>
       <listitem>
        <para>
         Sets the maximum number of workers that can be started by a single
         <literal>Gather</literal> node.  Parallel workers are taken from the
         pool of processes established by
         <xref linkend="guc-max-worker-processes">.  Note that the requested
         number of workers may not actually be available at run time.  If this
         occurs, the plan will run with fewer workers than expected, which may
         be inefficient.  Setting this value to 0, which is the default,
         disables parallel query execution.
        </para>

        <para>
         Note that parallel queries may consume very substantially more
         resources than non-parallel queries, because each worker process is
         a completely separate process which has roughly the same impact on the
         system as an additional user session.  This should be taken into
         account when choosing a value for this setting, as well as when
         configuring other settings that control resource utilization, such
         as <xref linkend="guc-work-mem">.  Resource limits such as
         <varname>work_mem</> are applied individually to each worker,
         which means the total utilization may be much higher across all
         processes than it would normally be for any single process.
         For example, a parallel query using 4 workers may use up to 5 times
         as much CPU time, memory, I/O bandwidth, and so forth as a query which
         uses no workers at all.
        </para>

        <para>
         For more information on parallel query, see
         <xref linkend="parallel-query">.
        </para>
       </listitem>
      </varlistentry>

      <varlistentry id="guc-backend-flush-after" xreflabel="backend_flush_after">
       <term><varname>backend_flush_after</varname> (<type>integer</type>)
       <indexterm>
        <primary><varname>backend_flush_after</> configuration parameter</primary>
       </indexterm>
       </term>
       <listitem>
        <para>
         Whenever more than <varname>backend_flush_after</varname> bytes have
         been written by a single backend, attempt to force the OS to issue
         these writes to the underlying storage.  Doing so will limit the
         amount of dirty data in the kernel's page cache, reducing the
         likelihood of stalls when an fsync is issued at the end of a
         checkpoint, or when the OS writes data back in larger batches in the
         background.  Often that will result in greatly reduced transaction
         latency, but there also are some cases, especially with workloads
         that are bigger than <xref linkend="guc-shared-buffers">, but smaller
         than the OS's page cache, where performance might degrade.  This
         setting may have no effect on some platforms.  The valid range is
         between <literal>0</literal>, which disables forced writeback,
         and <literal>2MB</literal>.  The default is <literal>0</>, i.e., no
         forced writeback.  (If <symbol>BLCKSZ</symbol> is not 8kB,
         the maximum value scales proportionally to it.)
        </para>
       </listitem>
      </varlistentry>

      <varlistentry id="guc-old-snapshot-threshold" xreflabel="old_snapshot_threshold">
       <term><varname>old_snapshot_threshold</varname> (<type>integer</type>)
       <indexterm>
        <primary><varname>old_snapshot_threshold</> configuration parameter</primary>
       </indexterm>
       </term>
       <listitem>
        <para>
         Sets the minimum time that a snapshot can be used without risk of a
         <literal>snapshot too old</> error occurring when using the snapshot.
         This parameter can only be set at server start.
        </para>

        <para>
         Beyond the threshold, old data may be vacuumed away.  This can help
         prevent bloat in the face of snapshots which remain in use for a
         long time.  To prevent incorrect results due to cleanup of data which
         would otherwise be visible to the snapshot, an error is generated
         when the snapshot is older than this threshold and the snapshot is
         used to read a page which has been modified since the snapshot was
         built.
        </para>

        <para>
         A value of <literal>-1</> disables this feature, and is the default.
         Useful values for production work probably range from a small number
         of hours to a few days.  The setting will be coerced to a granularity
         of minutes, and small numbers (such as <literal>0</> or
         <literal>1min</>) are only allowed because they may sometimes be
         useful for testing.  While a setting as high as <literal>60d</> is
         allowed, please note that in many workloads extreme bloat or
         transaction ID wraparound may occur in much shorter time frames.
        </para>

        <para>
         When this feature is enabled, freed space at the end of a relation
         cannot be released to the operating system, since that could remove
         information needed to detect the <literal>snapshot too old</>
         condition.  All space allocated to a relation remains associated with
         that relation for reuse only within that relation unless explicitly
         freed (for example, with <command>VACUUM FULL</>).
        </para>

        <para>
         This setting does not attempt to guarantee that an error will be
         generated under any particular circumstances.  In fact, if the
         correct results can be generated from (for example) a cursor which
         has materialized a result set, no error will be generated even if the
         underlying rows in the referenced table have been vacuumed away.
         Some tables cannot safely be vacuumed early, and so will not be
         affected by this setting.  Examples include system catalogs and any
         table which has a hash index.  For such tables this setting will
         neither reduce bloat nor create a possibility of a <literal>snapshot
         too old</> error on scanning.
        </para>
       </listitem>
      </varlistentry>
     </variablelist>
    </sect2>
   </sect1>

   <sect1 id="runtime-config-wal">
    <title>Write Ahead Log</title>

   <para>
    For additional information on tuning these settings,
    see <xref linkend="wal-configuration">.
   </para>

    <sect2 id="runtime-config-wal-settings">
     <title>Settings</title>
     <variablelist>

     <varlistentry id="guc-wal-level" xreflabel="wal_level">
      <term><varname>wal_level</varname> (<type>enum</type>)
      <indexterm>
       <primary><varname>wal_level</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        <varname>wal_level</> determines how much information is written
        to the WAL. The default value is <literal>minimal</>, which writes
        only the information needed to recover from a crash or immediate
        shutdown. <literal>replica</> adds logging required for WAL
        archiving as well as information required to run
        read-only queries on a standby server.  Finally,
        <literal>logical</> adds information necessary to support logical
        decoding.  Each level includes the information logged at all lower
        levels.  This parameter can only be set at server start.
       </para>
       <para>
        In <literal>minimal</> level, WAL-logging of some bulk
        operations can be safely skipped, which can make those
        operations much faster (see <xref linkend="populate-pitr">).
        Operations in which this optimization can be applied include:
        <simplelist>
         <member><command>CREATE TABLE AS</></member>
         <member><command>CREATE INDEX</></member>
         <member><command>CLUSTER</></member>
         <member><command>COPY</> into tables that were created or truncated in the same
         transaction</member>
        </simplelist>
        But minimal WAL does not contain enough information to reconstruct the
        data from a base backup and the WAL logs, so <literal>replica</> or
        higher must be used to enable WAL archiving
        (<xref linkend="guc-archive-mode">) and streaming replication.
       </para>
       <para>
        In <literal>logical</> level, the same information is logged as
        with <literal>replica</>, plus information needed to allow
        extracting logical change sets from the WAL. Using a level of
        <literal>logical</> will increase the WAL volume, particularly if many
        tables are configured for <literal>REPLICA IDENTITY FULL</literal> and
        many <command>UPDATE</> and <command>DELETE</> statements are
        executed.
       </para>
       <para>
        In releases prior to 9.6, this parameter also allowed the
        values <literal>archive</literal> and <literal>hot_standby</literal>.
        These are still accepted but mapped to <literal>replica</literal>.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-fsync" xreflabel="fsync">
      <term><varname>fsync</varname> (<type>boolean</type>)
      <indexterm>
       <primary><varname>fsync</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        If this parameter is on, the <productname>PostgreSQL</> server
        will try to make sure that updates are physically written to
        disk, by issuing <function>fsync()</> system calls or various
        equivalent methods (see <xref linkend="guc-wal-sync-method">).
        This ensures that the database cluster can recover to a
        consistent state after an operating system or hardware crash.
       </para>

       <para>
        While turning off <varname>fsync</varname> is often a performance
        benefit, this can result in unrecoverable data corruption in
        the event of a power failure or system crash.  Thus it
        is only advisable to turn off <varname>fsync</varname> if
        you can easily recreate your entire database from external
        data.
       </para>

       <para>
        Examples of safe circumstances for turning off
        <varname>fsync</varname> include the initial loading of a new
        database cluster from a backup file, using a database cluster
        for processing a batch of data after which the database
        will be thrown away and recreated,
        or for a read-only database clone which
        gets recreated frequently and is not used for failover.  High
        quality hardware alone is not a sufficient justification for
        turning off <varname>fsync</varname>.
       </para>

       <para>
        For reliable recovery when changing <varname>fsync</varname>
        off to on, it is necessary to force all modified buffers in the
        kernel to durable storage.  This can be done while the cluster
        is shutdown or while fsync is on by running <command>initdb
        --sync-only</command>, running <command>sync</>, unmounting the
        file system, or rebooting the server.
       </para>

       <para>
        In many situations, turning off <xref linkend="guc-synchronous-commit">
        for noncritical transactions can provide much of the potential
        performance benefit of turning off <varname>fsync</varname>, without
        the attendant risks of data corruption.
       </para>

       <para>
        <varname>fsync</varname> can only be set in the <filename>postgresql.conf</>
        file or on the server command line.
        If you turn this parameter off, also consider turning off
        <xref linkend="guc-full-page-writes">.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-synchronous-commit" xreflabel="synchronous_commit">
      <term><varname>synchronous_commit</varname> (<type>enum</type>)
      <indexterm>
       <primary><varname>synchronous_commit</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Specifies whether transaction commit will wait for WAL records
        to be written to disk before the command returns a <quote>success</>
        indication to the client.  Valid values are <literal>on</>,
        <literal>remote_apply</>, <literal>remote_write</>, <literal>local</>,
        and <literal>off</>.  The default, and safe, setting
        is <literal>on</>.  When <literal>off</>, there can be a delay between
        when success is reported to the client and when the transaction is
        really guaranteed to be safe against a server crash.  (The maximum
        delay is three times <xref linkend="guc-wal-writer-delay">.)  Unlike
        <xref linkend="guc-fsync">, setting this parameter to <literal>off</>
        does not create any risk of database inconsistency: an operating
        system or database crash might
        result in some recent allegedly-committed transactions being lost, but
        the database state will be just the same as if those transactions had
        been aborted cleanly.  So, turning <varname>synchronous_commit</> off
        can be a useful alternative when performance is more important than
        exact certainty about the durability of a transaction.  For more
        discussion see <xref linkend="wal-async-commit">.
       </para>
       <para>
        If <xref linkend="guc-synchronous-standby-names"> is non-empty, this
        parameter also controls whether or not transaction commits will wait
        for their WAL records to be replicated to the standby server(s).
        When set to <literal>on</>, commits will wait until replies
        from the current synchronous standby(s) indicate they have received
        the commit record of the transaction and flushed it to disk.  This
        ensures the transaction will not be lost unless both the primary and
        all synchronous standbys suffer corruption of their database storage.
        When set to <literal>remote_apply</>, commits will wait until replies
        from the current synchronous standby(s) indicate they have received the
        commit record of the transaction and applied it, so that it has become
        visible to queries on the standby(s).
        When set to <literal>remote_write</>, commits will wait until replies
        from the current synchronous standby(s) indicate they have
        received the commit record of the transaction and written it out to
        their operating system. This setting is sufficient to
        ensure data preservation even if a standby instance of
        <productname>PostgreSQL</> were to crash, but not if the standby
        suffers an operating-system-level crash, since the data has not
        necessarily reached stable storage on the standby.
        Finally, the setting <literal>local</> causes commits to wait for
        local flush to disk, but not for replication.  This is not usually
        desirable when synchronous replication is in use, but is provided for
        completeness.
       </para>
       <para>
        If <varname>synchronous_standby_names</> is empty, the settings
        <literal>on</>, <literal>remote_apply</>, <literal>remote_write</>
        and <literal>local</> all provide the same synchronization level:
        transaction commits only wait for local flush to disk.
       </para>
       <para>
        This parameter can be changed at any time; the behavior for any
        one transaction is determined by the setting in effect when it
        commits.  It is therefore possible, and useful, to have some
        transactions commit synchronously and others asynchronously.
        For example, to make a single multistatement transaction commit
        asynchronously when the default is the opposite, issue <command>SET
        LOCAL synchronous_commit TO OFF</> within the transaction.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-wal-sync-method" xreflabel="wal_sync_method">
      <term><varname>wal_sync_method</varname> (<type>enum</type>)
      <indexterm>
       <primary><varname>wal_sync_method</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Method used for forcing WAL updates out to disk.
        If <varname>fsync</varname> is off then this setting is irrelevant,
        since WAL file updates will not be forced out at all.
        Possible values are:
       </para>
       <itemizedlist>
        <listitem>
        <para>
         <literal>open_datasync</> (write WAL files with <function>open()</> option <symbol>O_DSYNC</>)
        </para>
        </listitem>
        <listitem>
        <para>
         <literal>fdatasync</> (call <function>fdatasync()</> at each commit)
        </para>
        </listitem>
        <listitem>
        <para>
         <literal>fsync</> (call <function>fsync()</> at each commit)
        </para>
        </listitem>
        <listitem>
        <para>
         <literal>fsync_writethrough</> (call <function>fsync()</> at each commit, forcing write-through of any disk write cache)
        </para>
        </listitem>
        <listitem>
        <para>
         <literal>open_sync</> (write WAL files with <function>open()</> option <symbol>O_SYNC</>)
        </para>
        </listitem>
       </itemizedlist>
       <para>
        The <literal>open_</>* options also use <literal>O_DIRECT</> if available.
        Not all of these choices are available on all platforms.
        The default is the first method in the above list that is supported
        by the platform, except that <literal>fdatasync</> is the default on
        Linux.  The default is not necessarily ideal; it might be
        necessary to change this setting or other aspects of your system
        configuration in order to create a crash-safe configuration or
        achieve optimal performance.
        These aspects are discussed in <xref linkend="wal-reliability">.
        This parameter can only be set in the <filename>postgresql.conf</>
        file or on the server command line.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-full-page-writes" xreflabel="full_page_writes">
      <term><varname>full_page_writes</varname> (<type>boolean</type>)
      <indexterm>
       <primary><varname>full_page_writes</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        When this parameter is on, the <productname>PostgreSQL</> server
        writes the entire content of each disk page to WAL during the
        first modification of that page after a checkpoint.
        This is needed because
        a page write that is in process during an operating system crash might
        be only partially completed, leading to an on-disk page
        that contains a mix of old and new data.  The row-level change data
        normally stored in WAL will not be enough to completely restore
        such a page during post-crash recovery.  Storing the full page image
        guarantees that the page can be correctly restored, but at the price
        of increasing the amount of data that must be written to WAL.
        (Because WAL replay always starts from a checkpoint, it is sufficient
        to do this during the first change of each page after a checkpoint.
        Therefore, one way to reduce the cost of full-page writes is to
        increase the checkpoint interval parameters.)
       </para>

       <para>
        Turning this parameter off speeds normal operation, but
        might lead to either unrecoverable data corruption, or silent
        data corruption, after a system failure. The risks are similar to turning off
        <varname>fsync</varname>, though smaller, and it should be turned off
        only based on the same circumstances recommended for that parameter.
       </para>

       <para>
        Turning off this parameter does not affect use of
        WAL archiving for point-in-time recovery (PITR)
        (see <xref linkend="continuous-archiving">).
       </para>

       <para>
        This parameter can only be set in the <filename>postgresql.conf</>
        file or on the server command line.
        The default is <literal>on</>.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-wal-log-hints" xreflabel="wal_log_hints">
      <term><varname>wal_log_hints</varname> (<type>boolean</type>)
      <indexterm>
       <primary><varname>wal_log_hints</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        When this parameter is <literal>on</>, the <productname>PostgreSQL</>
        server writes the entire content of each disk page to WAL during the
        first modification of that page after a checkpoint, even for
        non-critical modifications of so-called hint bits.
       </para>

       <para>
        If data checksums are enabled, hint bit updates are always WAL-logged
        and this setting is ignored. You can use this setting to test how much
        extra WAL-logging would occur if your database had data checksums
        enabled.
       </para>

       <para>
        This parameter can only be set at server start. The default value is <literal>off</>.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-wal-compression" xreflabel="wal_compression">
      <term><varname>wal_compression</varname> (<type>boolean</type>)
      <indexterm>
       <primary><varname>wal_compression</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        When this parameter is <literal>on</>, the <productname>PostgreSQL</>
        server compresses a full page image written to WAL when
        <xref linkend="guc-full-page-writes"> is on or during a base backup.
        A compressed page image will be decompressed during WAL replay.
        The default value is <literal>off</>.
        Only superusers can change this setting.
       </para>

       <para>
        Turning this parameter on can reduce the WAL volume without
        increasing the risk of unrecoverable data corruption,
        but at the cost of some extra CPU spent on the compression during
        WAL logging and on the decompression during WAL replay.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-wal-buffers" xreflabel="wal_buffers">
      <term><varname>wal_buffers</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>wal_buffers</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        The amount of shared memory used for WAL data that has not yet been
        written to disk.  The default setting of -1 selects a size equal to
        1/32nd (about 3%) of <xref linkend="guc-shared-buffers">, but not less
        than <literal>64kB</literal> nor more than the size of one WAL
        segment, typically <literal>16MB</literal>.  This value can be set
        manually if the automatic choice is too large or too small,
        but any positive value less than <literal>32kB</literal> will be
        treated as <literal>32kB</literal>.
        This parameter can only be set at server start.
       </para>

       <para>
        The contents of the WAL buffers are written out to disk at every
        transaction commit, so extremely large values are unlikely to
        provide a significant benefit.  However, setting this value to at
        least a few megabytes can improve write performance on a busy
        server where many clients are committing at once.  The auto-tuning
        selected by the default setting of -1 should give reasonable
        results in most cases.
       </para>

      </listitem>
     </varlistentry>

     <varlistentry id="guc-wal-writer-delay" xreflabel="wal_writer_delay">
      <term><varname>wal_writer_delay</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>wal_writer_delay</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
      <para>
        Specifies how often the WAL writer flushes WAL. After flushing WAL it
        sleeps for <varname>wal_writer_delay</> milliseconds, unless woken up
        by an asynchronously committing transaction. If the last flush
        happened less than <varname>wal_writer_delay</> milliseconds ago and
        less than <varname>wal_writer_flush_after</> bytes of WAL have been
        produced since, then WAL is only written to the operating system, not
        flushed to disk.
        The default value is 200 milliseconds (<literal>200ms</>).  Note that
        on many systems, the effective resolution of sleep delays is 10
        milliseconds; setting <varname>wal_writer_delay</> to a value that is
        not a multiple of 10 might have the same results as setting it to the
        next higher multiple of 10. This parameter can only be set in the
        <filename>postgresql.conf</> file or on the server command line.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-wal-writer-flush-after" xreflabel="wal_writer_flush_after">
      <term><varname>wal_writer_flush_after</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>wal_writer_flush_after</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
      <para>
        Specifies how often the WAL writer flushes WAL. If the last flush
        happened less than <varname>wal_writer_delay</> milliseconds ago and
        less than <varname>wal_writer_flush_after</> bytes of WAL have been
        produced since, then WAL is only written to the operating system, not
        flushed to disk.  If <varname>wal_writer_flush_after</> is set
        to <literal>0</> then WAL data is flushed immediately.  The default is
        <literal>1MB</literal>. This parameter can only be set in the
        <filename>postgresql.conf</> file or on the server command line.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-commit-delay" xreflabel="commit_delay">
      <term><varname>commit_delay</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>commit_delay</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        <varname>commit_delay</varname> adds a time delay, measured in
        microseconds, before a WAL flush is initiated.  This can improve
        group commit throughput by allowing a larger number of transactions
        to commit via a single WAL flush, if system load is high enough
        that additional transactions become ready to commit within the
        given interval.  However, it also increases latency by up to
        <varname>commit_delay</varname> microseconds for each WAL
        flush.  Because the delay is just wasted if no other transactions
        become ready to commit, a delay is only performed if at least
        <varname>commit_siblings</varname> other transactions are active
        when a flush is about to be initiated.  Also, no delays are
        performed if <varname>fsync</varname> is disabled.
        The default <varname>commit_delay</> is zero (no delay).
        Only superusers can change this setting.
       </para>
       <para>
        In <productname>PostgreSQL</> releases prior to 9.3,
        <varname>commit_delay</varname> behaved differently and was much
        less effective: it affected only commits, rather than all WAL flushes,
        and waited for the entire configured delay even if the WAL flush
        was completed sooner.  Beginning in <productname>PostgreSQL</> 9.3,
        the first process that becomes ready to flush waits for the configured
        interval, while subsequent processes wait only until the leader
        completes the flush operation.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-commit-siblings" xreflabel="commit_siblings">
      <term><varname>commit_siblings</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>commit_siblings</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Minimum number of concurrent open transactions to require
        before performing the <varname>commit_delay</> delay. A larger
        value makes it more probable that at least one other
        transaction will become ready to commit during the delay
        interval. The default is five transactions.
       </para>
      </listitem>
     </varlistentry>

     </variablelist>
     </sect2>
     <sect2 id="runtime-config-wal-checkpoints">
     <title>Checkpoints</title>

    <variablelist>
     <varlistentry id="guc-checkpoint-timeout" xreflabel="checkpoint_timeout">
      <term><varname>checkpoint_timeout</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>checkpoint_timeout</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Maximum time between automatic WAL checkpoints, in seconds.
        The valid range is between 30 seconds and one day.
        The default is five minutes (<literal>5min</>).
        Increasing this parameter can increase the amount of time needed
        for crash recovery.
        This parameter can only be set in the <filename>postgresql.conf</>
        file or on the server command line.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-checkpoint-completion-target" xreflabel="checkpoint_completion_target">
      <term><varname>checkpoint_completion_target</varname> (<type>floating point</type>)
      <indexterm>
       <primary><varname>checkpoint_completion_target</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Specifies the target of checkpoint completion, as a fraction of
        total time between checkpoints. The default is 0.5.
        This parameter can only be set in the <filename>postgresql.conf</>
        file or on the server command line.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-checkpoint-flush-after" xreflabel="checkpoint_flush_after">
      <term><varname>checkpoint_flush_after</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>checkpoint_flush_after</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Whenever more than <varname>checkpoint_flush_after</varname> bytes
        have been written while performing a checkpoint, attempt to force the
        OS to issue these writes to the underlying storage.  Doing so will
        limit the amount of dirty data in the kernel's page cache, reducing
        the likelihood of stalls when an fsync is issued at the end of the
        checkpoint, or when the OS writes data back in larger batches in the
        background.  Often that will result in greatly reduced transaction
        latency, but there also are some cases, especially with workloads
        that are bigger than <xref linkend="guc-shared-buffers">, but smaller
        than the OS's page cache, where performance might degrade.  This
        setting may have no effect on some platforms.  The valid range is
        between <literal>0</literal>, which disables forced writeback,
        and <literal>2MB</literal>.  The default is <literal>256kB</> on
        Linux, <literal>0</> elsewhere.  (If <symbol>BLCKSZ</symbol> is not
        8kB, the default and maximum values scale proportionally to it.)
        This parameter can only be set in the <filename>postgresql.conf</>
        file or on the server command line.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-checkpoint-warning" xreflabel="checkpoint_warning">
      <term><varname>checkpoint_warning</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>checkpoint_warning</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Write a message to the server log if checkpoints caused by
        the filling of checkpoint segment files happen closer together
        than this many seconds (which suggests that
        <varname>max_wal_size</> ought to be raised).  The default is
        30 seconds (<literal>30s</>).  Zero disables the warning.
        No warnings will be generated if <varname>checkpoint_timeout</varname>
        is less than <varname>checkpoint_warning</varname>.
        This parameter can only be set in the <filename>postgresql.conf</>
        file or on the server command line.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-max-wal-size" xreflabel="max_wal_size">
      <term><varname>max_wal_size</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>max_wal_size</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Maximum size to let the WAL grow to between automatic WAL
        checkpoints. This is a soft limit; WAL size can exceed
        <varname>max_wal_size</> under special circumstances, like
        under heavy load, a failing <varname>archive_command</>, or a high
        <varname>wal_keep_segments</> setting. The default is 1 GB.
        Increasing this parameter can increase the amount of time needed for
        crash recovery.
        This parameter can only be set in the <filename>postgresql.conf</>
        file or on the server command line.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-min-wal-size" xreflabel="min_wal_size">
      <term><varname>min_wal_size</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>min_wal_size</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        As long as WAL disk usage stays below this setting, old WAL files are
        always recycled for future use at a checkpoint, rather than removed.
        This can be used to ensure that enough WAL space is reserved to
        handle spikes in WAL usage, for example when running large batch
        jobs. The default is 80 MB.
        This parameter can only be set in the <filename>postgresql.conf</>
        file or on the server command line.
       </para>
      </listitem>
     </varlistentry>

     </variablelist>
     </sect2>
     <sect2 id="runtime-config-wal-archiving">
     <title>Archiving</title>

    <variablelist>
     <varlistentry id="guc-archive-mode" xreflabel="archive_mode">
      <term><varname>archive_mode</varname> (<type>enum</type>)
      <indexterm>
       <primary><varname>archive_mode</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        When <varname>archive_mode</> is enabled, completed WAL segments
        are sent to archive storage by setting
        <xref linkend="guc-archive-command">. In addition to <literal>off</>,
        to disable, there are two modes: <literal>on</>, and
        <literal>always</>. During normal operation, there is no
        difference between the two modes, but when set to <literal>always</>
        the WAL archiver is enabled also during archive recovery or standby
        mode. In <literal>always</> mode, all files restored from the archive
        or streamed with streaming replication will be archived (again). See
        <xref linkend="continuous-archiving-in-standby"> for details.
       </para>
       <para>
        <varname>archive_mode</> and <varname>archive_command</> are
        separate variables so that <varname>archive_command</> can be
        changed without leaving archiving mode.
        This parameter can only be set at server start.
        <varname>archive_mode</> cannot be enabled when
        <varname>wal_level</> is set to <literal>minimal</>.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-archive-command" xreflabel="archive_command">
      <term><varname>archive_command</varname> (<type>string</type>)
      <indexterm>
       <primary><varname>archive_command</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        The local shell command to execute to archive a completed WAL file
        segment.  Any <literal>%p</> in the string is
        replaced by the path name of the file to archive, and any
        <literal>%f</> is replaced by only the file name.
        (The path name is relative to the working directory of the server,
        i.e., the cluster's data directory.)
        Use <literal>%%</> to embed an actual <literal>%</> character in the
        command.  It is important for the command to return a zero
        exit status only if it succeeds. For more information see
        <xref linkend="backup-archiving-wal">.
       </para>
       <para>
        This parameter can only be set in the <filename>postgresql.conf</>
        file or on the server command line.  It is ignored unless
        <varname>archive_mode</> was enabled at server start.
        If <varname>archive_command</> is an empty string (the default) while
        <varname>archive_mode</> is enabled, WAL archiving is temporarily
        disabled, but the server continues to accumulate WAL segment files in
        the expectation that a command will soon be provided.  Setting
        <varname>archive_command</> to a command that does nothing but
        return true, e.g. <literal>/bin/true</> (<literal>REM</> on
        Windows), effectively disables
        archiving, but also breaks the chain of WAL files needed for
        archive recovery, so it should only be used in unusual circumstances.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-archive-timeout" xreflabel="archive_timeout">
      <term><varname>archive_timeout</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>archive_timeout</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        The <xref linkend="guc-archive-command"> is only invoked for
        completed WAL segments. Hence, if your server generates little WAL
        traffic (or has slack periods where it does so), there could be a
        long delay between the completion of a transaction and its safe
        recording in archive storage.  To limit how old unarchived
        data can be, you can set <varname>archive_timeout</> to force the
        server to switch to a new WAL segment file periodically.  When this
        parameter is greater than zero, the server will switch to a new
        segment file whenever this many seconds have elapsed since the last
        segment file switch, and there has been any database activity,
        including a single checkpoint.  (Increasing
        <varname>checkpoint_timeout</> will reduce unnecessary
        checkpoints on an idle system.)
        Note that archived files that are closed early
        due to a forced switch are still the same length as completely full
        files.  Therefore, it is unwise to use a very short
        <varname>archive_timeout</> &mdash; it will bloat your archive
        storage.  <varname>archive_timeout</> settings of a minute or so are
        usually reasonable.  You should consider using streaming replication,
        instead of archiving, if you want data to be copied off the master
        server more quickly than that.
        This parameter can only be set in the
        <filename>postgresql.conf</> file or on the server command line.
       </para>
      </listitem>
     </varlistentry>

     </variablelist>
    </sect2>

   </sect1>

   <sect1 id="runtime-config-replication">
    <title>Replication</title>

    <para>
     These settings control the behavior of the built-in
     <firstterm>streaming replication</> feature (see
     <xref linkend="streaming-replication">).  Servers will be either a
     Master or a Standby server.  Masters can send data, while Standby(s)
     are always receivers of replicated data.  When cascading replication
     (see <xref linkend="cascading-replication">) is used, Standby server(s)
     can also be senders, as well as receivers.
     Parameters are mainly for Sending and Standby servers, though some
     parameters have meaning only on the Master server.  Settings may vary
     across the cluster without problems if that is required.
    </para>

    <sect2 id="runtime-config-replication-sender">
     <title>Sending Server(s)</title>

     <para>
      These parameters can be set on any server that is
      to send replication data to one or more standby servers.
      The master is always a sending server, so these parameters must
      always be set on the master.
      The role and meaning of these parameters does not change after a
      standby becomes the master.
     </para>

     <variablelist>
      <varlistentry id="guc-max-wal-senders" xreflabel="max_wal_senders">
       <term><varname>max_wal_senders</varname> (<type>integer</type>)
       <indexterm>
        <primary><varname>max_wal_senders</> configuration parameter</primary>
       </indexterm>
       </term>
       <listitem>
       <para>
        Specifies the maximum number of concurrent connections from
        standby servers or streaming base backup clients (i.e., the
        maximum number of simultaneously running WAL sender
        processes). The default is zero, meaning replication is
        disabled. WAL sender processes count towards the total number
        of connections, so the parameter cannot be set higher than
        <xref linkend="guc-max-connections">.  Abrupt streaming client
        disconnection might cause an orphaned connection slot until
        a timeout is reached, so this parameter should be set slightly
        higher than the maximum number of expected clients so disconnected
        clients can immediately reconnect.  This parameter can only
        be set at server start. <varname>wal_level</> must be set to
        <literal>replica</> or higher to allow connections from standby
        servers.
       </para>
       </listitem>
      </varlistentry>

      <varlistentry id="guc-max-replication-slots" xreflabel="max_replication_slots">
       <term><varname>max_replication_slots</varname> (<type>integer</type>)
       <indexterm>
        <primary><varname>max_replication_slots</> configuration parameter</primary>
       </indexterm>
       </term>
       <listitem>
        <para>
         Specifies the maximum number of replication slots
         (see <xref linkend="streaming-replication-slots">) that the server
         can support. The default is zero.  This parameter can only be set at
         server start.
         <varname>wal_level</varname> must be set
         to <literal>replica</literal> or higher to allow replication slots to
         be used. Setting it to a lower value than the number of currently
         existing replication slots will prevent the server from starting.
        </para>
       </listitem>
      </varlistentry>

      <varlistentry id="guc-wal-keep-segments" xreflabel="wal_keep_segments">
       <term><varname>wal_keep_segments</varname> (<type>integer</type>)
       <indexterm>
        <primary><varname>wal_keep_segments</> configuration parameter</primary>
       </indexterm>
       </term>
       <listitem>
       <para>
        Specifies the minimum number of past log file segments kept in the
        <filename>pg_xlog</>
        directory, in case a standby server needs to fetch them for streaming
        replication. Each segment is normally 16 megabytes. If a standby
        server connected to the sending server falls behind by more than
        <varname>wal_keep_segments</> segments, the sending server might remove
        a WAL segment still needed by the standby, in which case the
        replication connection will be terminated.  Downstream connections
        will also eventually fail as a result.  (However, the standby
        server can recover by fetching the segment from archive, if WAL
        archiving is in use.)
       </para>

       <para>
        This sets only the minimum number of segments retained in
        <filename>pg_xlog</>; the system might need to retain more segments
        for WAL archival or to recover from a checkpoint. If
        <varname>wal_keep_segments</> is zero (the default), the system
        doesn't keep any extra segments for standby purposes, so the number
        of old WAL segments available to standby servers is a function of
        the location of the previous checkpoint and status of WAL
        archiving.
        This parameter can only be set in the
        <filename>postgresql.conf</> file or on the server command line.
       </para>
       </listitem>
      </varlistentry>

     <varlistentry id="guc-wal-sender-timeout" xreflabel="wal_sender_timeout">
      <term><varname>wal_sender_timeout</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>wal_sender_timeout</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Terminate replication connections that are inactive longer
        than the specified number of milliseconds. This is useful for
        the sending server to detect a standby crash or network outage.
        A value of zero disables the timeout mechanism.  This parameter
        can only be set in
        the <filename>postgresql.conf</> file or on the server command line.
        The default value is 60 seconds.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-track-commit-timestamp" xreflabel="track_commit_timestamp">
      <term><varname>track_commit_timestamp</varname> (<type>bool</type>)
      <indexterm>
       <primary><varname>track_commit_timestamp</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Record commit time of transactions. This parameter
        can only be set in <filename>postgresql.conf</> file or on the server
        command line. The default value is <literal>off</literal>.
       </para>
      </listitem>
     </varlistentry>

     </variablelist>
    </sect2>

    <sect2 id="runtime-config-replication-master">
     <title>Master Server</title>

     <para>
      These parameters can be set on the master/primary server that is
      to send replication data to one or more standby servers.
      Note that in addition to these parameters,
      <xref linkend="guc-wal-level"> must be set appropriately on the master
      server, and optionally WAL archiving can be enabled as
      well (see <xref linkend="runtime-config-wal-archiving">).
      The values of these parameters on standby servers are irrelevant,
      although you may wish to set them there in preparation for the
      possibility of a standby becoming the master.
     </para>

    <variablelist>

     <varlistentry id="guc-synchronous-standby-names" xreflabel="synchronous_standby_names">
      <term><varname>synchronous_standby_names</varname> (<type>string</type>)
      <indexterm>
       <primary><varname>synchronous_standby_names</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Specifies a list of standby servers that can support
        <firstterm>synchronous replication</>, as described in
        <xref linkend="synchronous-replication">.
        There will be one or more active synchronous standbys;
        transactions waiting for commit will be allowed to proceed after
        these standby servers confirm receipt of their data.
        The synchronous standbys will be those whose names appear
        earlier in this list, and
        that are both currently connected and streaming data in real-time
        (as shown by a state of <literal>streaming</literal> in the
        <link linkend="pg-stat-replication-view">
        <literal>pg_stat_replication</></link> view).
        Other standby servers appearing later in this list represent potential
        synchronous standbys. If any of the current synchronous
        standbys disconnects for whatever reason,
        it will be replaced immediately with the next-highest-priority standby.
        Specifying more than one standby name can allow very high availability.
       </para>
       <para>
        This parameter specifies a list of standby servers using
        either of the following syntaxes:
<synopsis>
<replaceable class="parameter">num_sync</replaceable> ( <replaceable class="parameter">standby_name</replaceable> [, ...] )
<replaceable class="parameter">standby_name</replaceable> [, ...]
</synopsis>
        where <replaceable class="parameter">num_sync</replaceable> is
        the number of synchronous standbys that transactions need to
        wait for replies from,
        and <replaceable class="parameter">standby_name</replaceable>
        is the name of a standby server. For example, a setting of
        <literal>3 (s1, s2, s3, s4)</> makes transaction commits wait
        until their WAL records are received by three higher-priority standbys
        chosen from standby servers <literal>s1</>, <literal>s2</>,
        <literal>s3</> and <literal>s4</>.
        </para>
        <para>
        The second syntax was used before <productname>PostgreSQL</>
        version 9.6 and is still supported. It's the same as the first syntax
        with <replaceable class="parameter">num_sync</replaceable> equal to 1.
        For example, <literal>1 (s1, s2)</> and
        <literal>s1, s2</> have the same meaning: either <literal>s1</>
        or <literal>s2</> is chosen as a synchronous standby.
       </para>
       <para>
        The name of a standby server for this purpose is the
        <varname>application_name</> setting of the standby, as set in the
        <varname>primary_conninfo</> of the standby's WAL receiver.  There is
        no mechanism to enforce uniqueness. In case of duplicates one of the
        matching standbys will be considered as higher priority, though
        exactly which one is indeterminate.
        The special entry <literal>*</> matches any
        <varname>application_name</>, including the default application name
        of <literal>walreceiver</>.
       </para>
       <note>
        <para>
         Each <replaceable class="parameter">standby_name</replaceable>
         should have the form of a valid SQL identifier, unless it
         is <literal>*</>.  You can use double-quoting if necessary.  But note
         that <replaceable class="parameter">standby_name</replaceable>s are
         compared to standby application names case-insensitively, whether
         double-quoted or not.
        </para>
       </note>
       <para>
        If no synchronous standby names are specified here, then synchronous
        replication is not enabled and transaction commits will not wait for
        replication.  This is the default configuration.  Even when
        synchronous replication is enabled, individual transactions can be
        configured not to wait for replication by setting the
        <xref linkend="guc-synchronous-commit"> parameter to
        <literal>local</> or <literal>off</>.
       </para>
       <para>
        This parameter can only be set in the <filename>postgresql.conf</>
        file or on the server command line.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-vacuum-defer-cleanup-age" xreflabel="vacuum_defer_cleanup_age">
      <term><varname>vacuum_defer_cleanup_age</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>vacuum_defer_cleanup_age</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Specifies the number of transactions by which <command>VACUUM</> and
        <acronym>HOT</> updates will defer cleanup of dead row versions. The
        default is zero transactions, meaning that dead row versions can be
        removed as soon as possible, that is, as soon as they are no longer
        visible to any open transaction.  You may wish to set this to a
        non-zero value on a primary server that is supporting hot standby
        servers, as described in <xref linkend="hot-standby">.  This allows
        more time for queries on the standby to complete without incurring
        conflicts due to early cleanup of rows.  However, since the value
        is measured in terms of number of write transactions occurring on the
        primary server, it is difficult to predict just how much additional
        grace time will be made available to standby queries.
        This parameter can only be set in the <filename>postgresql.conf</>
        file or on the server command line.
       </para>
       <para>
        You should also consider setting <varname>hot_standby_feedback</>
        on standby server(s) as an alternative to using this parameter.
       </para>
       <para>
        This does not prevent cleanup of dead rows which have reached the age
        specified by <varname>old_snapshot_threshold</>.
       </para>
      </listitem>
     </varlistentry>

     </variablelist>
    </sect2>

    <sect2 id="runtime-config-replication-standby">
     <title>Standby Servers</title>

     <para>
      These settings control the behavior of a standby server that is
      to receive replication data.  Their values on the master server
      are irrelevant.
     </para>

    <variablelist>

     <varlistentry id="guc-hot-standby" xreflabel="hot_standby">
      <term><varname>hot_standby</varname> (<type>boolean</type>)
      <indexterm>
       <primary><varname>hot_standby</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Specifies whether or not you can connect and run queries during
        recovery, as described in <xref linkend="hot-standby">.
        The default value is <literal>off</literal>.
        This parameter can only be set at server start. It only has effect
        during archive recovery or in standby mode.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-max-standby-archive-delay" xreflabel="max_standby_archive_delay">
      <term><varname>max_standby_archive_delay</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>max_standby_archive_delay</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        When Hot Standby is active, this parameter determines how long the
        standby server should wait before canceling standby queries that
        conflict with about-to-be-applied WAL entries, as described in
        <xref linkend="hot-standby-conflict">.
        <varname>max_standby_archive_delay</> applies when WAL data is
        being read from WAL archive (and is therefore not current).
        The default is 30 seconds. Units are milliseconds if not specified.
        A value of -1 allows the standby to wait forever for conflicting
        queries to complete.
        This parameter can only be set in the <filename>postgresql.conf</>
        file or on the server command line.
       </para>
       <para>
        Note that <varname>max_standby_archive_delay</> is not the same as the
        maximum length of time a query can run before cancellation; rather it
        is the maximum total time allowed to apply any one WAL segment's data.
        Thus, if one query has resulted in significant delay earlier in the
        WAL segment, subsequent conflicting queries will have much less grace
        time.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-max-standby-streaming-delay" xreflabel="max_standby_streaming_delay">
      <term><varname>max_standby_streaming_delay</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>max_standby_streaming_delay</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        When Hot Standby is active, this parameter determines how long the
        standby server should wait before canceling standby queries that
        conflict with about-to-be-applied WAL entries, as described in
        <xref linkend="hot-standby-conflict">.
        <varname>max_standby_streaming_delay</> applies when WAL data is
        being received via streaming replication.
        The default is 30 seconds. Units are milliseconds if not specified.
        A value of -1 allows the standby to wait forever for conflicting
        queries to complete.
        This parameter can only be set in the <filename>postgresql.conf</>
        file or on the server command line.
       </para>
       <para>
        Note that <varname>max_standby_streaming_delay</> is not the same as
        the maximum length of time a query can run before cancellation; rather
        it is the maximum total time allowed to apply WAL data once it has
        been received from the primary server.  Thus, if one query has
        resulted in significant delay, subsequent conflicting queries will
        have much less grace time until the standby server has caught up
        again.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-wal-receiver-status-interval" xreflabel="wal_receiver_status_interval">
      <term><varname>wal_receiver_status_interval</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>wal_receiver_status_interval</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
      <para>
       Specifies the minimum frequency for the WAL receiver
       process on the standby to send information about replication progress
       to the primary or upstream standby, where it can be seen using the
       <link linkend="pg-stat-replication-view">
       <literal>pg_stat_replication</></link> view.  The standby will report
       the last transaction log position it has written, the last position it
       has flushed to disk, and the last position it has applied.
       This parameter's
       value is the maximum interval, in seconds, between reports.  Updates are
       sent each time the write or flush positions change, or at least as
       often as specified by this parameter.  Thus, the apply position may
       lag slightly behind the true position.  Setting this parameter to zero
       disables status updates completely.  This parameter can only be set in
       the <filename>postgresql.conf</> file or on the server command line.
       The default value is 10 seconds.
      </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-hot-standby-feedback" xreflabel="hot_standby_feedback">
      <term><varname>hot_standby_feedback</varname> (<type>boolean</type>)
      <indexterm>
       <primary><varname>hot_standby_feedback</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Specifies whether or not a hot standby will send feedback to the primary
        or upstream standby
        about queries currently executing on the standby. This parameter can
        be used to eliminate query cancels caused by cleanup records, but
        can cause database bloat on the primary for some workloads.
        Feedback messages will not be sent more frequently than once per
        <varname>wal_receiver_status_interval</>. The default value is
        <literal>off</literal>. This parameter can only be set in the
        <filename>postgresql.conf</> file or on the server command line.
       </para>
       <para>
        If cascaded replication is in use the feedback is passed upstream
        until it eventually reaches the primary.  Standbys make no other use
        of feedback they receive other than to pass upstream.
       </para>
       <para>
        This setting does not override the behavior of
        <varname>old_snapshot_threshold</> on the primary; a snapshot on the
        standby which exceeds the primary's age threshold can become invalid,
        resulting in cancellation of transactions on the standby.  This is
        because <varname>old_snapshot_threshold</> is intended to provide an
        absolute limit on the time which dead rows can contribute to bloat,
        which would otherwise be violated because of the configuration of a
        standby.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-wal-receiver-timeout" xreflabel="wal_receiver_timeout">
      <term><varname>wal_receiver_timeout</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>wal_receiver_timeout</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Terminate replication connections that are inactive longer
        than the specified number of milliseconds. This is useful for
        the receiving standby server to detect a primary node crash or network
        outage.
        A value of zero disables the timeout mechanism.  This parameter
        can only be set in
        the <filename>postgresql.conf</> file or on the server command line.
        The default value is 60 seconds.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-wal-retrieve-retry-interval" xreflabel="wal_retrieve_retry_interval">
      <term><varname>wal_retrieve_retry_interval</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>wal_retrieve_retry_interval</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Specify how long the standby server should wait when WAL data is not
        available from any sources (streaming replication,
        local <filename>pg_xlog</> or WAL archive) before retrying to
        retrieve WAL data.  This parameter can only be set in the
        <filename>postgresql.conf</> file or on the server command line.
        The default value is 5 seconds. Units are milliseconds if not specified.
       </para>
       <para>
        This parameter is useful in configurations where a node in recovery
        needs to control the amount of time to wait for new WAL data to be
        available. For example, in archive recovery, it is possible to
        make the recovery more responsive in the detection of a new WAL
        log file by reducing the value of this parameter. On a system with
        low WAL activity, increasing it reduces the amount of requests necessary
        to access WAL archives, something useful for example in cloud
        environments where the amount of times an infrastructure is accessed
        is taken into account.
       </para>
      </listitem>
     </varlistentry>

     </variablelist>
    </sect2>
   </sect1>

   <sect1 id="runtime-config-query">
    <title>Query Planning</title>

    <sect2 id="runtime-config-query-enable">
     <title>Planner Method Configuration</title>

      <para>
       These configuration parameters provide a crude method of
       influencing the query plans chosen by the query optimizer. If
       the default plan chosen by the optimizer for a particular query
       is not optimal, a <emphasis>temporary</> solution is to use one
       of these configuration parameters to force the optimizer to
       choose a different plan.
       Better ways to improve the quality of the
       plans chosen by the optimizer include adjusting the planer cost
       constants (see <xref linkend="runtime-config-query-constants">),
       running <xref linkend="sql-analyze"> manually, increasing
       the value of the <xref
       linkend="guc-default-statistics-target"> configuration parameter,
       and increasing the amount of statistics collected for
       specific columns using <command>ALTER TABLE SET
       STATISTICS</command>.
      </para>

     <variablelist>
     <varlistentry id="guc-enable-bitmapscan" xreflabel="enable_bitmapscan">
      <term><varname>enable_bitmapscan</varname> (<type>boolean</type>)
      <indexterm>
       <primary>bitmap scan</primary>
      </indexterm>
      <indexterm>
       <primary><varname>enable_bitmapscan</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Enables or disables the query planner's use of bitmap-scan plan
        types. The default is <literal>on</>.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-enable-hashagg" xreflabel="enable_hashagg">
      <term><varname>enable_hashagg</varname> (<type>boolean</type>)
      <indexterm>
       <primary><varname>enable_hashagg</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Enables or disables the query planner's use of hashed
        aggregation plan types. The default is <literal>on</>.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-enable-hashjoin" xreflabel="enable_hashjoin">
      <term><varname>enable_hashjoin</varname> (<type>boolean</type>)
      <indexterm>
       <primary><varname>enable_hashjoin</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Enables or disables the query planner's use of hash-join plan
        types. The default is <literal>on</>.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-enable-indexscan" xreflabel="enable_indexscan">
      <term><varname>enable_indexscan</varname> (<type>boolean</type>)
      <indexterm>
       <primary>index scan</primary>
      </indexterm>
      <indexterm>
       <primary><varname>enable_indexscan</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Enables or disables the query planner's use of index-scan plan
        types. The default is <literal>on</>.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-enable-indexonlyscan" xreflabel="enable_indexonlyscan">
      <term><varname>enable_indexonlyscan</varname> (<type>boolean</type>)
      <indexterm>
       <primary><varname>enable_indexonlyscan</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Enables or disables the query planner's use of index-only-scan plan
        types (see <xref linkend="indexes-index-only-scans">).
        The default is <literal>on</>.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-enable-material" xreflabel="enable_material">
      <term><varname>enable_material</varname> (<type>boolean</type>)
      <indexterm>
       <primary><varname>enable_material</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Enables or disables the query planner's use of materialization.
        It is impossible to suppress materialization entirely,
        but turning this variable off prevents the planner from inserting
        materialize nodes except in cases where it is required for correctness.
        The default is <literal>on</>.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-enable-mergejoin" xreflabel="enable_mergejoin">
      <term><varname>enable_mergejoin</varname> (<type>boolean</type>)
      <indexterm>
       <primary><varname>enable_mergejoin</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Enables or disables the query planner's use of merge-join plan
        types. The default is <literal>on</>.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-enable-nestloop" xreflabel="enable_nestloop">
      <term><varname>enable_nestloop</varname> (<type>boolean</type>)
      <indexterm>
       <primary><varname>enable_nestloop</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Enables or disables the query planner's use of nested-loop join
        plans. It is impossible to suppress nested-loop joins entirely,
        but turning this variable off discourages the planner from using
        one if there are other methods available. The default is
        <literal>on</>.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-enable-seqscan" xreflabel="enable_seqscan">
      <term><varname>enable_seqscan</varname> (<type>boolean</type>)
      <indexterm>
       <primary>sequential scan</primary>
      </indexterm>
      <indexterm>
       <primary><varname>enable_seqscan</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Enables or disables the query planner's use of sequential scan
        plan types. It is impossible to suppress sequential scans
        entirely, but turning this variable off discourages the planner
        from using one if there are other methods available. The
        default is <literal>on</>.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-enable-sort" xreflabel="enable_sort">
      <term><varname>enable_sort</varname> (<type>boolean</type>)
      <indexterm>
       <primary><varname>enable_sort</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Enables or disables the query planner's use of explicit sort
        steps. It is impossible to suppress explicit sorts entirely,
        but turning this variable off discourages the planner from
        using one if there are other methods available. The default
        is <literal>on</>.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-enable-tidscan" xreflabel="enable_tidscan">
      <term><varname>enable_tidscan</varname> (<type>boolean</type>)
      <indexterm>
       <primary><varname>enable_tidscan</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Enables or disables the query planner's use of <acronym>TID</>
        scan plan types. The default is <literal>on</>.
       </para>
      </listitem>
     </varlistentry>

     </variablelist>
     </sect2>
     <sect2 id="runtime-config-query-constants">
     <title>Planner Cost Constants</title>

    <para>
     The <firstterm>cost</> variables described in this section are measured
     on an arbitrary scale.  Only their relative values matter, hence
     scaling them all up or down by the same factor will result in no change
     in the planner's choices.  By default, these cost variables are based on
     the cost of sequential page fetches; that is,
     <varname>seq_page_cost</> is conventionally set to <literal>1.0</>
     and the other cost variables are set with reference to that.  But
     you can use a different scale if you prefer, such as actual execution
     times in milliseconds on a particular machine.
    </para>

   <note>
    <para>
     Unfortunately, there is no well-defined method for determining ideal
     values for the cost variables.  They are best treated as averages over
     the entire mix of queries that a particular installation will receive.  This
     means that changing them on the basis of just a few experiments is very
     risky.
    </para>
   </note>

     <variablelist>

     <varlistentry id="guc-seq-page-cost" xreflabel="seq_page_cost">
      <term><varname>seq_page_cost</varname> (<type>floating point</type>)
      <indexterm>
       <primary><varname>seq_page_cost</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Sets the planner's estimate of the cost of a disk page fetch
        that is part of a series of sequential fetches.  The default is 1.0.
        This value can be overridden for tables and indexes in a particular
        tablespace by setting the tablespace parameter of the same name
        (see <xref linkend="sql-altertablespace">).
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-random-page-cost" xreflabel="random_page_cost">
      <term><varname>random_page_cost</varname> (<type>floating point</type>)
      <indexterm>
       <primary><varname>random_page_cost</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Sets the planner's estimate of the cost of a
        non-sequentially-fetched disk page.  The default is 4.0.
        This value can be overridden for tables and indexes in a particular
        tablespace by setting the tablespace parameter of the same name
        (see <xref linkend="sql-altertablespace">).
       </para>

       <para>
        Reducing this value relative to <varname>seq_page_cost</>
        will cause the system to prefer index scans; raising it will
        make index scans look relatively more expensive.  You can raise
        or lower both values together to change the importance of disk I/O
        costs relative to CPU costs, which are described by the following
        parameters.
       </para>

       <para>
        Random access to mechanical disk storage is normally much more expensive
        than four times sequential access.  However, a lower default is used
        (4.0) because the majority of random accesses to disk, such as indexed
        reads, are assumed to be in cache.  The default value can be thought of
        as modeling random access as 40 times slower than sequential, while
        expecting 90% of random reads to be cached.
       </para>

       <para>
        If you believe a 90% cache rate is an incorrect assumption
        for your workload, you can increase random_page_cost to better
        reflect the true cost of random storage reads. Correspondingly,
        if your data is likely to be completely in cache, such as when
        the database is smaller than the total server memory, decreasing
        random_page_cost can be appropriate.  Storage that has a low random
        read cost relative to sequential, e.g. solid-state drives, might
        also be better modeled with a lower value for random_page_cost.
       </para>

       <tip>
        <para>
         Although the system will let you set <varname>random_page_cost</> to
         less than <varname>seq_page_cost</>, it is not physically sensible
         to do so.  However, setting them equal makes sense if the database
         is entirely cached in RAM, since in that case there is no penalty
         for touching pages out of sequence.  Also, in a heavily-cached
         database you should lower both values relative to the CPU parameters,
         since the cost of fetching a page already in RAM is much smaller
         than it would normally be.
        </para>
       </tip>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-cpu-tuple-cost" xreflabel="cpu_tuple_cost">
      <term><varname>cpu_tuple_cost</varname> (<type>floating point</type>)
      <indexterm>
       <primary><varname>cpu_tuple_cost</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Sets the planner's estimate of the cost of processing
        each row during a query.
        The default is 0.01.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-cpu-index-tuple-cost" xreflabel="cpu_index_tuple_cost">
      <term><varname>cpu_index_tuple_cost</varname> (<type>floating point</type>)
      <indexterm>
       <primary><varname>cpu_index_tuple_cost</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Sets the planner's estimate of the cost of processing
        each index entry during an index scan.
        The default is 0.005.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-cpu-operator-cost" xreflabel="cpu_operator_cost">
      <term><varname>cpu_operator_cost</varname> (<type>floating point</type>)
      <indexterm>
       <primary><varname>cpu_operator_cost</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Sets the planner's estimate of the cost of processing each
        operator or function executed during a query.
        The default is 0.0025.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-parallel-setup-cost" xreflabel="parallel_setup_cost">
      <term><varname>parallel_setup_cost</varname> (<type>floating point</type>)
      <indexterm>
       <primary><varname>parallel_setup_cost</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Sets the planner's estimate of the cost of launching parallel worker
        processes.
        The default is 1000.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-parallel-tuple-cost" xreflabel="parallel_tuple_cost">
      <term><varname>parallel_tuple_cost</varname> (<type>floating point</type>)
      <indexterm>
       <primary><varname>parallel_tuple_cost</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Sets the planner's estimate of the cost of transferring one tuple
        from a parallel worker process to another process.
        The default is 0.1.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-min-parallel-relation-size" xreflabel="min_parallel_relation_size">
      <term><varname>min_parallel_relation_size</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>min_parallel_relation_size</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Sets the minimum size of relations to be considered for parallel scan.
        The default is 8 megabytes (<literal>8MB</>).
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-effective-cache-size" xreflabel="effective_cache_size">
      <term><varname>effective_cache_size</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>effective_cache_size</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Sets the planner's assumption about the effective size of the
        disk cache that is available to a single query.  This is
        factored into estimates of the cost of using an index; a
        higher value makes it more likely index scans will be used, a
        lower value makes it more likely sequential scans will be
        used. When setting this parameter you should consider both
        <productname>PostgreSQL</productname>'s shared buffers and the
        portion of the kernel's disk cache that will be used for
        <productname>PostgreSQL</productname> data files, though some
        data might exist in both places. Also, take
        into account the expected number of concurrent queries on different
        tables, since they will have to share the available
        space.  This parameter has no effect on the size of shared
        memory allocated by <productname>PostgreSQL</productname>, nor
        does it reserve kernel disk cache; it is used only for estimation
        purposes.  The system also does not assume data remains in
        the disk cache between queries.  The default is 4 gigabytes
        (<literal>4GB</>).
       </para>
      </listitem>
     </varlistentry>

     </variablelist>

    </sect2>
     <sect2 id="runtime-config-query-geqo">
     <title>Genetic Query Optimizer</title>

     <para>
      The genetic query optimizer (GEQO) is an algorithm that does query
      planning using heuristic searching.  This reduces planning time for
      complex queries (those joining many relations), at the cost of producing
      plans that are sometimes inferior to those found by the normal
      exhaustive-search algorithm.
      For more information see <xref linkend="geqo">.
     </para>

     <variablelist>

     <varlistentry id="guc-geqo" xreflabel="geqo">
      <term><varname>geqo</varname> (<type>boolean</type>)
      <indexterm>
       <primary>genetic query optimization</primary>
      </indexterm>
      <indexterm>
       <primary>GEQO</primary>
       <see>genetic query optimization</see>
      </indexterm>
      <indexterm>
       <primary><varname>geqo</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Enables or disables genetic query optimization.
        This is on by default.  It is usually best not to turn it off in
        production; the <varname>geqo_threshold</varname> variable provides
        more granular control of GEQO.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-geqo-threshold" xreflabel="geqo_threshold">
      <term><varname>geqo_threshold</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>geqo_threshold</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Use genetic query optimization to plan queries with at least
        this many <literal>FROM</> items involved. (Note that a
        <literal>FULL OUTER JOIN</> construct counts as only one <literal>FROM</>
        item.) The default is 12. For simpler queries it is usually best
        to use the regular, exhaustive-search planner, but for queries with
        many tables the exhaustive search takes too long, often
        longer than the penalty of executing a suboptimal plan.  Thus,
        a threshold on the size of the query is a convenient way to manage
        use of GEQO.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-geqo-effort" xreflabel="geqo_effort">
      <term><varname>geqo_effort</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>geqo_effort</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Controls the trade-off between planning time and query plan
        quality in GEQO. This variable must be an integer in the
        range from 1 to 10. The default value is five. Larger values
        increase the time spent doing query planning, but also
        increase the likelihood that an efficient query plan will be
        chosen.
       </para>

       <para>
        <varname>geqo_effort</varname> doesn't actually do anything
        directly; it is only used to compute the default values for
        the other variables that influence GEQO behavior (described
        below). If you prefer, you can set the other parameters by
        hand instead.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-geqo-pool-size" xreflabel="geqo_pool_size">
      <term><varname>geqo_pool_size</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>geqo_pool_size</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Controls the pool size used by GEQO, that is the
        number of individuals in the genetic population.  It must be
        at least two, and useful values are typically 100 to 1000.  If
        it is set to zero (the default setting) then a suitable
        value is chosen based on <varname>geqo_effort</varname> and
        the number of tables in the query.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-geqo-generations" xreflabel="geqo_generations">
      <term><varname>geqo_generations</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>geqo_generations</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Controls the number of generations used by GEQO, that is
        the number of iterations of the algorithm.  It must
        be at least one, and useful values are in the same range as
        the pool size.  If it is set to zero (the default setting)
        then a suitable value is chosen based on
        <varname>geqo_pool_size</varname>.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-geqo-selection-bias" xreflabel="geqo_selection_bias">
      <term><varname>geqo_selection_bias</varname> (<type>floating point</type>)
      <indexterm>
       <primary><varname>geqo_selection_bias</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Controls the selection bias used by GEQO. The selection bias
        is the selective pressure within the population. Values can be
        from 1.50 to 2.00; the latter is the default.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-geqo-seed" xreflabel="geqo_seed">
      <term><varname>geqo_seed</varname> (<type>floating point</type>)
      <indexterm>
       <primary><varname>geqo_seed</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Controls the initial value of the random number generator used
        by GEQO to select random paths through the join order search space.
        The value can range from zero (the default) to one.  Varying the
        value changes the set of join paths explored, and may result in a
        better or worse best path being found.
       </para>
      </listitem>
     </varlistentry>

     </variablelist>
    </sect2>
     <sect2 id="runtime-config-query-other">
     <title>Other Planner Options</title>

     <variablelist>

     <varlistentry id="guc-default-statistics-target" xreflabel="default_statistics_target">
      <term><varname>default_statistics_target</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>default_statistics_target</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Sets the default statistics target for table columns without
        a column-specific target set via <command>ALTER TABLE
        SET STATISTICS</>.  Larger values increase the time needed to
        do <command>ANALYZE</>, but might improve the quality of the
        planner's estimates. The default is 100. For more information
        on the use of statistics by the <productname>PostgreSQL</>
        query planner, refer to <xref linkend="planner-stats">.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-constraint-exclusion" xreflabel="constraint_exclusion">
      <term><varname>constraint_exclusion</varname> (<type>enum</type>)
      <indexterm>
       <primary>constraint exclusion</primary>
      </indexterm>
      <indexterm>
       <primary><varname>constraint_exclusion</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Controls the query planner's use of table constraints to
        optimize queries.
        The allowed values of <varname>constraint_exclusion</> are
        <literal>on</> (examine constraints for all tables),
        <literal>off</> (never examine constraints), and
        <literal>partition</> (examine constraints only for inheritance child
        tables and <literal>UNION ALL</> subqueries).
        <literal>partition</> is the default setting.
        It is often used with inheritance and partitioned tables to
        improve performance.
      </para>

       <para>
        When this parameter allows it for a particular table, the planner
        compares query conditions with the table's <literal>CHECK</>
        constraints, and omits scanning tables for which the conditions
        contradict the constraints.  For example:

<programlisting>
CREATE TABLE parent(key integer, ...);
CREATE TABLE child1000(check (key between 1000 and 1999)) INHERITS(parent);
CREATE TABLE child2000(check (key between 2000 and 2999)) INHERITS(parent);
...
SELECT * FROM parent WHERE key = 2400;
</programlisting>

        With constraint exclusion enabled, this <command>SELECT</>
        will not scan <structname>child1000</> at all, improving performance.
       </para>

       <para>
        Currently, constraint exclusion is enabled by default
        only for cases that are often used to implement table partitioning.
        Turning it on for all tables imposes extra planning overhead that is
        quite noticeable on simple queries, and most often will yield no
        benefit for simple queries.  If you have no partitioned tables
        you might prefer to turn it off entirely.
       </para>

       <para>
        Refer to <xref linkend="ddl-partitioning-constraint-exclusion"> for
        more information on using constraint exclusion and partitioning.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-cursor-tuple-fraction" xreflabel="cursor_tuple_fraction">
      <term><varname>cursor_tuple_fraction</varname> (<type>floating point</type>)
      <indexterm>
       <primary><varname>cursor_tuple_fraction</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Sets the planner's estimate of the fraction of a cursor's rows that
        will be retrieved.  The default is 0.1.  Smaller values of this
        setting bias the planner towards using <quote>fast start</> plans
        for cursors, which will retrieve the first few rows quickly while
        perhaps taking a long time to fetch all rows.  Larger values
        put more emphasis on the total estimated time.  At the maximum
        setting of 1.0, cursors are planned exactly like regular queries,
        considering only the total estimated time and not how soon the
        first rows might be delivered.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-from-collapse-limit" xreflabel="from_collapse_limit">
      <term><varname>from_collapse_limit</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>from_collapse_limit</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        The planner will merge sub-queries into upper queries if the
        resulting <literal>FROM</literal> list would have no more than
        this many items.  Smaller values reduce planning time but might
        yield inferior query plans.  The default is eight.
        For more information see <xref linkend="explicit-joins">.
       </para>

       <para>
        Setting this value to <xref linkend="guc-geqo-threshold"> or more
        may trigger use of the GEQO planner, resulting in non-optimal
        plans.  See <xref linkend="runtime-config-query-geqo">.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-join-collapse-limit" xreflabel="join_collapse_limit">
      <term><varname>join_collapse_limit</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>join_collapse_limit</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        The planner will rewrite explicit <literal>JOIN</>
        constructs (except <literal>FULL JOIN</>s) into lists of
        <literal>FROM</> items whenever a list of no more than this many items
        would result.  Smaller values reduce planning time but might
        yield inferior query plans.
       </para>

       <para>
        By default, this variable is set the same as
        <varname>from_collapse_limit</varname>, which is appropriate
        for most uses. Setting it to 1 prevents any reordering of
        explicit <literal>JOIN</>s. Thus, the explicit join order
        specified in the query will be the actual order in which the
        relations are joined. Because the query planner does not always choose
        the optimal join order, advanced users can elect to
        temporarily set this variable to 1, and then specify the join
        order they desire explicitly.
        For more information see <xref linkend="explicit-joins">.
       </para>

       <para>
        Setting this value to <xref linkend="guc-geqo-threshold"> or more
        may trigger use of the GEQO planner, resulting in non-optimal
        plans.  See <xref linkend="runtime-config-query-geqo">.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-force-parallel-mode" xreflabel="force_parallel_mode">
      <term><varname>force_parallel_mode</varname> (<type>enum</type>)
      <indexterm>
       <primary><varname>force_parallel_mode</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Allows the use of parallel queries for testing purposes even in cases
        where no performance benefit is expected.
        The allowed values of <varname>force_parallel_mode</> are
        <literal>off</> (use parallel mode only when it is expected to improve
        performance), <literal>on</> (force parallel query for all queries
        for which it is thought to be safe), and <literal>regress</> (like
        <literal>on</>, but with additional behavior changes as explained
        below).
       </para>

       <para>
        More specifically, setting this value to <literal>on</> will add
        a <literal>Gather</> node to the top of any query plan for which this
        appears to be safe, so that the query runs inside of a parallel worker.
        Even when a parallel worker is not available or cannot be used,
        operations such as starting a subtransaction that would be prohibited
        in a parallel query context will be prohibited unless the planner
        believes that this will cause the query to fail.  If failures or
        unexpected results occur when this option is set, some functions used
        by the query may need to be marked <literal>PARALLEL UNSAFE</literal>
        (or, possibly, <literal>PARALLEL RESTRICTED</literal>).
       </para>

       <para>
        Setting this value to <literal>regress</> has all of the same effects
        as setting it to <literal>on</> plus some additional effects that are
        intended to facilitate automated regression testing.  Normally,
        messages from a parallel worker include a context line indicating that,
        but a setting of <literal>regress</> suppresses this line so that the
        output is the same as in non-parallel execution.  Also,
        the <literal>Gather</> nodes added to plans by this setting are hidden
        in <literal>EXPLAIN</> output so that the output matches what
        would be obtained if this setting were turned <literal>off</>.
       </para>
      </listitem>
     </varlistentry>

     </variablelist>
    </sect2>
   </sect1>

   <sect1 id="runtime-config-logging">
    <title>Error Reporting and Logging</title>

    <indexterm zone="runtime-config-logging">
     <primary>server log</primary>
    </indexterm>

    <sect2 id="runtime-config-logging-where">
     <title>Where To Log</title>

     <indexterm zone="runtime-config-logging-where">
      <primary>where to log</primary>
     </indexterm>

     <variablelist>

     <varlistentry id="guc-log-destination" xreflabel="log_destination">
      <term><varname>log_destination</varname> (<type>string</type>)
      <indexterm>
       <primary><varname>log_destination</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        <productname>PostgreSQL</productname> supports several methods
         for logging server messages, including
         <systemitem>stderr</systemitem>, <systemitem>csvlog</systemitem> and
         <systemitem>syslog</systemitem>. On Windows,
         <systemitem>eventlog</systemitem> is also supported. Set this
         parameter to a list of desired log destinations separated by
         commas. The default is to log to <systemitem>stderr</systemitem>
         only.
         This parameter can only be set in the <filename>postgresql.conf</>
         file or on the server command line.
       </para>
       <para>
        If <systemitem>csvlog</> is included in <varname>log_destination</>,
        log entries are output in <quote>comma separated
        value</> (<acronym>CSV</>) format, which is convenient for
        loading logs into programs.
        See <xref linkend="runtime-config-logging-csvlog"> for details.
        <xref linkend="guc-logging-collector"> must be enabled to generate
        CSV-format log output.
       </para>

       <note>
        <para>
         On most Unix systems, you will need to alter the configuration of
         your system's <application>syslog</application> daemon in order
         to make use of the <systemitem>syslog</systemitem> option for
         <varname>log_destination</>.  <productname>PostgreSQL</productname>
         can log to <application>syslog</application> facilities
         <literal>LOCAL0</> through <literal>LOCAL7</> (see <xref
         linkend="guc-syslog-facility">), but the default
         <application>syslog</application> configuration on most platforms
         will discard all such messages.  You will need to add something like:
<programlisting>
local0.*    /var/log/postgresql
</programlisting>
         to the  <application>syslog</application> daemon's configuration file
         to make it work.
        </para>
        <para>
         On Windows, when you use the <literal>eventlog</literal>
         option for <varname>log_destination</>, you should
         register an event source and its library with the operating
         system so that the Windows Event Viewer can display event
         log messages cleanly.
         See <xref linkend="event-log-registration"> for details.
        </para>
       </note>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-logging-collector" xreflabel="logging_collector">
      <term><varname>logging_collector</varname> (<type>boolean</type>)
      <indexterm>
       <primary><varname>logging_collector</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
         This parameter enables the <firstterm>logging collector</>, which
         is a background process that captures log messages
         sent to <systemitem>stderr</> and redirects them into log files.
         This approach is often more useful than
         logging to <application>syslog</>, since some types of messages
         might not appear in <application>syslog</> output.  (One common
         example is dynamic-linker failure messages; another is error messages
         produced by scripts such as <varname>archive_command</>.)
         This parameter can only be set at server start.
       </para>

       <note>
        <para>
         It is possible to log to <systemitem>stderr</> without using the
         logging collector; the log messages will just go to wherever the
         server's <systemitem>stderr</> is directed.  However, that method is
         only suitable for low log volumes, since it provides no convenient
         way to rotate log files.  Also, on some platforms not using the
         logging collector can result in lost or garbled log output, because
         multiple processes writing concurrently to the same log file can
         overwrite each other's output.
        </para>
       </note>

       <note>
        <para>
          The logging collector is designed to never lose messages.  This means
          that in case of extremely high load, server processes could be
          blocked while trying to send additional log messages when the
          collector has fallen behind.  In contrast, <application>syslog</>
          prefers to drop messages if it cannot write them, which means it
          may fail to log some messages in such cases but it will not block
          the rest of the system.
        </para>
       </note>

      </listitem>
     </varlistentry>

     <varlistentry id="guc-log-directory" xreflabel="log_directory">
      <term><varname>log_directory</varname> (<type>string</type>)
      <indexterm>
       <primary><varname>log_directory</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        When <varname>logging_collector</> is enabled,
        this parameter determines the directory in which log files will be created.
        It can be specified as an absolute path, or relative to the
        cluster data directory.
        This parameter can only be set in the <filename>postgresql.conf</>
        file or on the server command line.
        The default is <literal>pg_log</literal>.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-log-filename" xreflabel="log_filename">
      <term><varname>log_filename</varname> (<type>string</type>)
      <indexterm>
       <primary><varname>log_filename</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        When <varname>logging_collector</varname> is enabled,
        this parameter sets the file names of the created log files.  The value
        is treated as a <function>strftime</function> pattern,
        so <literal>%</literal>-escapes can be used to specify time-varying
        file names.  (Note that if there are
        any time-zone-dependent <literal>%</literal>-escapes, the computation
        is done in the zone specified
        by <xref linkend="guc-log-timezone">.)
        The supported <literal>%</literal>-escapes are similar to those
        listed in the Open Group's <ulink
        url="http://pubs.opengroup.org/onlinepubs/009695399/functions/strftime.html">strftime
        </ulink> specification.
        Note that the system's <function>strftime</function> is not used
        directly, so platform-specific (nonstandard) extensions do not work.
        The default is <literal>postgresql-%Y-%m-%d_%H%M%S.log</literal>.
       </para>
       <para>
        If you specify a file name without escapes, you should plan to
        use a log rotation utility to avoid eventually filling the
        entire disk.  In releases prior to 8.4, if
        no <literal>%</literal> escapes were
        present, <productname>PostgreSQL</productname> would append
        the epoch of the new log file's creation time, but this is no
        longer the case.
       </para>
       <para>
        If CSV-format output is enabled in <varname>log_destination</>,
        <literal>.csv</> will be appended to the timestamped
        log file name to create the file name for CSV-format output.
        (If <varname>log_filename</> ends in <literal>.log</>, the suffix is
        replaced instead.)
       </para>
       <para>
        This parameter can only be set in the <filename>postgresql.conf</>
        file or on the server command line.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-log-file-mode" xreflabel="log_file_mode">
      <term><varname>log_file_mode</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>log_file_mode</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        On Unix systems this parameter sets the permissions for log files
        when <varname>logging_collector</varname> is enabled. (On Microsoft
        Windows this parameter is ignored.)
        The parameter value is expected to be a numeric mode
        specified in the format accepted by the
        <function>chmod</function> and <function>umask</function>
        system calls.  (To use the customary octal format the number
        must start with a <literal>0</literal> (zero).)
       </para>
       <para>
        The default permissions are <literal>0600</>, meaning only the
        server owner can read or write the log files.  The other commonly
        useful setting is <literal>0640</>, allowing members of the owner's
        group to read the files.  Note however that to make use of such a
        setting, you'll need to alter <xref linkend="guc-log-directory"> to
        store the files somewhere outside the cluster data directory.  In
        any case, it's unwise to make the log files world-readable, since
        they might contain sensitive data.
       </para>
       <para>
        This parameter can only be set in the <filename>postgresql.conf</>
        file or on the server command line.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-log-rotation-age" xreflabel="log_rotation_age">
      <term><varname>log_rotation_age</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>log_rotation_age</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        When <varname>logging_collector</varname> is enabled,
        this parameter determines the maximum lifetime of an individual log file.
        After this many minutes have elapsed, a new log file will
        be created.  Set to zero to disable time-based creation of
        new log files.
        This parameter can only be set in the <filename>postgresql.conf</>
        file or on the server command line.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-log-rotation-size" xreflabel="log_rotation_size">
      <term><varname>log_rotation_size</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>log_rotation_size</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        When <varname>logging_collector</varname> is enabled,
        this parameter determines the maximum size of an individual log file.
        After this many kilobytes have been emitted into a log file,
        a new log file will be created.  Set to zero to disable size-based
        creation of new log files.
        This parameter can only be set in the <filename>postgresql.conf</>
        file or on the server command line.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-log-truncate-on-rotation" xreflabel="log_truncate_on_rotation">
      <term><varname>log_truncate_on_rotation</varname> (<type>boolean</type>)
      <indexterm>
       <primary><varname>log_truncate_on_rotation</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        When <varname>logging_collector</varname> is enabled,
        this parameter will cause <productname>PostgreSQL</productname> to truncate (overwrite),
        rather than append to, any existing log file of the same name.
        However, truncation will occur only when a new file is being opened
        due to time-based rotation, not during server startup or size-based
        rotation.  When off, pre-existing files will be appended to in
        all cases.  For example, using this setting in combination with
        a <varname>log_filename</varname> like <literal>postgresql-%H.log</literal>
        would result in generating twenty-four hourly log files and then
        cyclically overwriting them.
        This parameter can only be set in the <filename>postgresql.conf</>
        file or on the server command line.
       </para>
       <para>
        Example:  To keep 7 days of logs, one log file per day named
        <literal>server_log.Mon</literal>, <literal>server_log.Tue</literal>,
        etc, and automatically overwrite last week's log with this week's log,
        set <varname>log_filename</varname> to <literal>server_log.%a</literal>,
        <varname>log_truncate_on_rotation</varname> to <literal>on</literal>, and
        <varname>log_rotation_age</varname> to <literal>1440</literal>.
       </para>
       <para>
        Example: To keep 24 hours of logs, one log file per hour, but
        also rotate sooner if the log file size exceeds 1GB, set
        <varname>log_filename</varname> to <literal>server_log.%H%M</literal>,
        <varname>log_truncate_on_rotation</varname> to <literal>on</literal>,
        <varname>log_rotation_age</varname> to <literal>60</literal>, and
        <varname>log_rotation_size</varname> to <literal>1000000</literal>.
        Including <literal>%M</> in <varname>log_filename</varname> allows
        any size-driven rotations that might occur to select a file name
        different from the hour's initial file name.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-syslog-facility" xreflabel="syslog_facility">
      <term><varname>syslog_facility</varname> (<type>enum</type>)
      <indexterm>
       <primary><varname>syslog_facility</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        When logging to <application>syslog</> is enabled, this parameter
        determines the <application>syslog</application>
        <quote>facility</quote> to be used.  You can choose
        from <literal>LOCAL0</>, <literal>LOCAL1</>,
        <literal>LOCAL2</>, <literal>LOCAL3</>, <literal>LOCAL4</>,
        <literal>LOCAL5</>, <literal>LOCAL6</>, <literal>LOCAL7</>;
        the default is <literal>LOCAL0</>. See also the
        documentation of your system's
        <application>syslog</application> daemon.
        This parameter can only be set in the <filename>postgresql.conf</>
        file or on the server command line.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-syslog-ident" xreflabel="syslog_ident">
      <term><varname>syslog_ident</varname> (<type>string</type>)
      <indexterm>
       <primary><varname>syslog_ident</> configuration parameter</primary>
      </indexterm>
      </term>
       <listitem>
        <para>
         When logging to <application>syslog</> is enabled, this parameter
         determines the program name used to identify
         <productname>PostgreSQL</productname> messages in
         <application>syslog</application> logs. The default is
         <literal>postgres</literal>.
         This parameter can only be set in the <filename>postgresql.conf</>
         file or on the server command line.
        </para>
       </listitem>
      </varlistentry>

      <varlistentry id="guc-syslog-sequence-numbers" xreflabel="syslog_sequence_numbers">
       <term><varname>syslog_sequence_numbers</varname> (<type>boolean</type>)
        <indexterm>
         <primary><varname>syslog_sequence_numbers</> configuration parameter</primary>
        </indexterm>
       </term>

       <listitem>
        <para>
         When logging to <application>syslog</application> and this is on (the
         default), then each message will be prefixed by an increasing
         sequence number (such as <literal>[2]</literal>).  This circumvents
         the <quote>--- last message repeated N times ---</quote> suppression
         that many syslog implementations perform by default.  In more modern
         syslog implementations, repeated message suppression can be configured
         (for example, <literal>$RepeatedMsgReduction</literal>
         in <productname>rsyslog</productname>), so this might not be
         necessary.  Also, you could turn this off if you actually want to
         suppress repeated messages.
        </para>

        <para>
         This parameter can only be set in the <filename>postgresql.conf</>
         file or on the server command line.
        </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-syslog-split-messages" xreflabel="syslog_split_messages">
      <term><varname>syslog_split_messages</varname> (<type>boolean</type>)
      <indexterm>
       <primary><varname>syslog_split_messages</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        When logging to <application>syslog</> is enabled, this parameter
        determines how messages are delivered to syslog.  When on (the
        default), messages are split by lines, and long lines are split so
        that they will fit into 1024 bytes, which is a typical size limit for
        traditional syslog implementations.  When off, PostgreSQL server log
        messages are delivered to the syslog service as is, and it is up to
        the syslog service to cope with the potentially bulky messages.
       </para>

       <para>
        If syslog is ultimately logging to a text file, then the effect will
        be the same either way, and it is best to leave the setting on, since
        most syslog implementations either cannot handle large messages or
        would need to be specially configured to handle them.  But if syslog
        is ultimately writing into some other medium, it might be necessary or
        more useful to keep messages logically together.
       </para>

       <para>
        This parameter can only be set in the <filename>postgresql.conf</>
        file or on the server command line.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-event-source" xreflabel="event_source">
      <term><varname>event_source</varname> (<type>string</type>)
      <indexterm>
       <primary><varname>event_source</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        When logging to <application>event log</> is enabled, this parameter
        determines the program name used to identify
        <productname>PostgreSQL</productname> messages in
        the log. The default is <literal>PostgreSQL</literal>.
        This parameter can only be set in the <filename>postgresql.conf</>
        file or on the server command line.
       </para>
      </listitem>
     </varlistentry>

      </variablelist>
    </sect2>
     <sect2 id="runtime-config-logging-when">
     <title>When To Log</title>

     <variablelist>

     <varlistentry id="guc-client-min-messages" xreflabel="client_min_messages">
      <term><varname>client_min_messages</varname> (<type>enum</type>)
      <indexterm>
       <primary><varname>client_min_messages</varname> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Controls which message levels are sent to the client.
        Valid values are <literal>DEBUG5</literal>,
        <literal>DEBUG4</literal>, <literal>DEBUG3</literal>, <literal>DEBUG2</literal>,
        <literal>DEBUG1</literal>, <literal>LOG</literal>, <literal>NOTICE</literal>,
        <literal>WARNING</literal>, <literal>ERROR</literal>, <literal>FATAL</literal>,
        and <literal>PANIC</literal>.  Each level
        includes all the levels that follow it.  The later the level,
        the fewer messages are sent.  The default is
        <literal>NOTICE</literal>.  Note that <literal>LOG</literal> has a different
        rank here than in <varname>log_min_messages</varname>.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-log-min-messages" xreflabel="log_min_messages">
      <term><varname>log_min_messages</varname> (<type>enum</type>)
      <indexterm>
       <primary><varname>log_min_messages</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Controls which <link linkend="runtime-config-severity-levels">message
        levels</link> are written to the server log.
        Valid values are <literal>DEBUG5</literal>, <literal>DEBUG4</literal>,
        <literal>DEBUG3</literal>, <literal>DEBUG2</literal>, <literal>DEBUG1</literal>,
        <literal>INFO</literal>, <literal>NOTICE</literal>, <literal>WARNING</literal>,
        <literal>ERROR</literal>, <literal>LOG</literal>, <literal>FATAL</literal>, and
        <literal>PANIC</literal>.  Each level includes all the levels that
        follow it.  The later the level, the fewer messages are sent
        to the log.  The default is <literal>WARNING</>.  Note that
        <literal>LOG</> has a different rank here than in
        <xref linkend="guc-client-min-messages">.
        Only superusers can change this setting.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-log-min-error-statement" xreflabel="log_min_error_statement">
      <term><varname>log_min_error_statement</varname> (<type>enum</type>)
      <indexterm>
       <primary><varname>log_min_error_statement</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Controls which SQL statements that cause an error
        condition are recorded in the server log.  The current
        SQL statement is included in the log entry for any message of
        the specified
        <link linkend="runtime-config-severity-levels">severity</link>
        or higher.
        Valid values are <literal>DEBUG5</literal>,
        <literal>DEBUG4</literal>, <literal>DEBUG3</literal>,
        <literal>DEBUG2</literal>, <literal>DEBUG1</literal>,
        <literal>INFO</literal>, <literal>NOTICE</literal>,
        <literal>WARNING</literal>, <literal>ERROR</literal>,
        <literal>LOG</literal>,
        <literal>FATAL</literal>, and <literal>PANIC</literal>.
        The default is <literal>ERROR</literal>, which means statements
        causing errors, log messages, fatal errors, or panics will be logged.
        To effectively turn off logging of failing statements,
        set this parameter to <literal>PANIC</literal>.
        Only superusers can change this setting.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-log-min-duration-statement" xreflabel="log_min_duration_statement">
      <term><varname>log_min_duration_statement</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>log_min_duration_statement</> configuration parameter</primary>
      </indexterm>
      </term>
       <listitem>
        <para>
         Causes the duration of each completed statement to be logged
         if the statement ran for at least the specified number of
         milliseconds.  Setting this to zero prints all statement durations.
         Minus-one (the default) disables logging statement durations.
         For example, if you set it to <literal>250ms</literal>
         then all SQL statements that run 250ms or longer will be
         logged.  Enabling this parameter can be helpful in tracking down
         unoptimized queries in your applications.
         Only superusers can change this setting.
        </para>

        <para>
         For clients using extended query protocol, durations of the Parse,
         Bind, and Execute steps are logged independently.
        </para>

       <note>
        <para>
         When using this option together with
         <xref linkend="guc-log-statement">,
         the text of statements that are logged because of
         <varname>log_statement</> will not be repeated in the
         duration log message.
         If you are not using <application>syslog</>, it is recommended
         that you log the PID or session ID using
         <xref linkend="guc-log-line-prefix">
         so that you can link the statement message to the later
         duration message using the process ID or session ID.
        </para>
       </note>
       </listitem>
      </varlistentry>

     </variablelist>

    <para>
     <xref linkend="runtime-config-severity-levels"> explains the message
     severity levels used by <productname>PostgreSQL</>.  If logging output
     is sent to <systemitem>syslog</systemitem> or Windows'
     <systemitem>eventlog</systemitem>, the severity levels are translated
     as shown in the table.
    </para>

    <table id="runtime-config-severity-levels">
     <title>Message Severity Levels</title>
     <tgroup cols="4">
      <thead>
       <row>
        <entry>Severity</entry>
        <entry>Usage</entry>
        <entry><systemitem>syslog</></entry>
        <entry><systemitem>eventlog</></entry>
       </row>
      </thead>

      <tbody>
       <row>
        <entry><literal>DEBUG1..DEBUG5</></entry>
        <entry>Provides successively-more-detailed information for use by
         developers.</entry>
        <entry><literal>DEBUG</></entry>
        <entry><literal>INFORMATION</></entry>
       </row>

       <row>
        <entry><literal>INFO</></entry>
        <entry>Provides information implicitly requested by the user,
         e.g., output from <command>VACUUM VERBOSE</>.</entry>
        <entry><literal>INFO</></entry>
        <entry><literal>INFORMATION</></entry>
       </row>

       <row>
        <entry><literal>NOTICE</></entry>
        <entry>Provides information that might be helpful to users, e.g.,
         notice of truncation of long identifiers.</entry>
        <entry><literal>NOTICE</></entry>
        <entry><literal>INFORMATION</></entry>
       </row>

       <row>
        <entry><literal>WARNING</></entry>
        <entry>Provides warnings of likely problems, e.g., <command>COMMIT</>
         outside a transaction block.</entry>
        <entry><literal>NOTICE</></entry>
        <entry><literal>WARNING</></entry>
       </row>

       <row>
        <entry><literal>ERROR</></entry>
        <entry>Reports an error that caused the current command to
         abort.</entry>
        <entry><literal>WARNING</></entry>
        <entry><literal>ERROR</></entry>
       </row>

       <row>
        <entry><literal>LOG</></entry>
        <entry>Reports information of interest to administrators, e.g.,
         checkpoint activity.</entry>
        <entry><literal>INFO</></entry>
        <entry><literal>INFORMATION</></entry>
       </row>

       <row>
        <entry><literal>FATAL</></entry>
        <entry>Reports an error that caused the current session to
         abort.</entry>
        <entry><literal>ERR</></entry>
        <entry><literal>ERROR</></entry>
       </row>

       <row>
        <entry><literal>PANIC</></entry>
        <entry>Reports an error that caused all database sessions to abort.</entry>
        <entry><literal>CRIT</></entry>
        <entry><literal>ERROR</></entry>
       </row>
      </tbody>
     </tgroup>
    </table>

    </sect2>
     <sect2 id="runtime-config-logging-what">
     <title>What To Log</title>

     <variablelist>

     <varlistentry id="guc-application-name" xreflabel="application_name">
      <term><varname>application_name</varname> (<type>string</type>)
      <indexterm>
       <primary><varname>application_name</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        The <varname>application_name</varname> can be any string of less than
        <symbol>NAMEDATALEN</> characters (64 characters in a standard build).
        It is typically set by an application upon connection to the server.
        The name will be displayed in the <structname>pg_stat_activity</> view
        and included in CSV log entries.  It can also be included in regular
        log entries via the <xref linkend="guc-log-line-prefix"> parameter.
        Only printable ASCII characters may be used in the
        <varname>application_name</varname> value. Other characters will be
        replaced with question marks (<literal>?</literal>).
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><varname>debug_print_parse</varname> (<type>boolean</type>)
      <indexterm>
       <primary><varname>debug_print_parse</> configuration parameter</primary>
      </indexterm>
      </term>
      <term><varname>debug_print_rewritten</varname> (<type>boolean</type>)
      <indexterm>
       <primary><varname>debug_print_rewritten</> configuration parameter</primary>
      </indexterm>
      </term>
      <term><varname>debug_print_plan</varname> (<type>boolean</type>)
      <indexterm>
       <primary><varname>debug_print_plan</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        These parameters enable various debugging output to be emitted.
        When set, they print the resulting parse tree, the query rewriter
        output, or the execution plan for each executed query.
        These messages are emitted at <literal>LOG</> message level, so by
        default they will appear in the server log but will not be sent to the
        client.  You can change that by adjusting
        <xref linkend="guc-client-min-messages"> and/or
        <xref linkend="guc-log-min-messages">.
        These parameters are off by default.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><varname>debug_pretty_print</varname> (<type>boolean</type>)
      <indexterm>
       <primary><varname>debug_pretty_print</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        When set, <varname>debug_pretty_print</varname> indents the messages
        produced by <varname>debug_print_parse</varname>,
        <varname>debug_print_rewritten</varname>, or
        <varname>debug_print_plan</varname>.  This results in more readable
        but much longer output than the <quote>compact</> format used when
        it is off.  It is on by default.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-log-checkpoints" xreflabel="log_checkpoints">
      <term><varname>log_checkpoints</varname> (<type>boolean</type>)
      <indexterm>
       <primary><varname>log_checkpoints</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Causes checkpoints and restartpoints to be logged in the server log.
        Some statistics are included in the log messages, including the number
        of buffers written and the time spent writing them.
        This parameter can only be set in the <filename>postgresql.conf</>
        file or on the server command line. The default is off.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-log-connections" xreflabel="log_connections">
      <term><varname>log_connections</varname> (<type>boolean</type>)
      <indexterm>
       <primary><varname>log_connections</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Causes each attempted connection to the server to be logged,
        as well as successful completion of client authentication.
        Only superusers can change this parameter at session start,
        and it cannot be changed at all within a session.
        The default is <literal>off</>.
       </para>

       <note>
        <para>
         Some client programs, like <application>psql</>, attempt
         to connect twice while determining if a password is required, so
         duplicate <quote>connection received</> messages do not
         necessarily indicate a problem.
        </para>
       </note>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-log-disconnections" xreflabel="log_disconnections">
      <term><varname>log_disconnections</varname> (<type>boolean</type>)
      <indexterm>
       <primary><varname>log_disconnections</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Causes session terminations to be logged.  The log output
        provides information similar to <varname>log_connections</varname>,
        plus the duration of the session.
        Only superusers can change this parameter at session start,
        and it cannot be changed at all within a session.
        The default is <literal>off</>.
       </para>
      </listitem>
     </varlistentry>


     <varlistentry id="guc-log-duration" xreflabel="log_duration">
      <term><varname>log_duration</varname> (<type>boolean</type>)
      <indexterm>
       <primary><varname>log_duration</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Causes the duration of every completed statement to be logged.
        The default is <literal>off</>.
        Only superusers can change this setting.
       </para>

       <para>
        For clients using extended query protocol, durations of the Parse,
        Bind, and Execute steps are logged independently.
       </para>

       <note>
        <para>
         The difference between setting this option and setting
         <xref linkend="guc-log-min-duration-statement"> to zero is that
         exceeding <varname>log_min_duration_statement</> forces the text of
         the query to be logged, but this option doesn't.  Thus, if
         <varname>log_duration</> is <literal>on</> and
         <varname>log_min_duration_statement</> has a positive value, all
         durations are logged but the query text is included only for
         statements exceeding the threshold.  This behavior can be useful for
         gathering statistics in high-load installations.
        </para>
       </note>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-log-error-verbosity" xreflabel="log_error_verbosity">
      <term><varname>log_error_verbosity</varname> (<type>enum</type>)
      <indexterm>
       <primary><varname>log_error_verbosity</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Controls the amount of detail written in the server log for each
        message that is logged.  Valid values are <literal>TERSE</>,
        <literal>DEFAULT</>, and <literal>VERBOSE</>, each adding more
        fields to displayed messages.  <literal>TERSE</> excludes
        the logging of <literal>DETAIL</>, <literal>HINT</>,
        <literal>QUERY</>, and <literal>CONTEXT</> error information.
        <literal>VERBOSE</> output includes the <symbol>SQLSTATE</> error
        code (see also <xref linkend="errcodes-appendix">) and the source code file name, function name,
        and line number that generated the error.
        Only superusers can change this setting.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-log-hostname" xreflabel="log_hostname">
      <term><varname>log_hostname</varname> (<type>boolean</type>)
      <indexterm>
       <primary><varname>log_hostname</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        By default, connection log messages only show the IP address of the
        connecting host. Turning this parameter on causes logging of the
        host name as well.  Note that depending on your host name resolution
        setup this might impose a non-negligible performance penalty.
        This parameter can only be set in the <filename>postgresql.conf</>
        file or on the server command line.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-log-line-prefix" xreflabel="log_line_prefix">
      <term><varname>log_line_prefix</varname> (<type>string</type>)
      <indexterm>
       <primary><varname>log_line_prefix</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
         This is a <function>printf</>-style string that is output at the
         beginning of each log line.
         <literal>%</> characters begin <quote>escape sequences</>
         that are replaced with status information as outlined below.
         Unrecognized escapes are ignored. Other
         characters are copied straight to the log line. Some escapes are
         only recognized by session processes, and will be treated as empty by
         background processes such as the main server process. Status
         information may be aligned either left or right by specifying a
         numeric literal after the % and before the option. A negative
         value will cause the status information to be padded on the
         right with spaces to give it a minimum width, whereas a positive
         value will pad on the left. Padding can be useful to aid human
         readability in log files.
         This parameter can only be set in the <filename>postgresql.conf</>
         file or on the server command line. The default is an empty string.

         <informaltable>
          <tgroup cols="3">
           <thead>
            <row>
             <entry>Escape</entry>
             <entry>Effect</entry>
             <entry>Session only</entry>
             </row>
            </thead>
           <tbody>
            <row>
             <entry><literal>%a</literal></entry>
             <entry>Application name</entry>
             <entry>yes</entry>
            </row>
            <row>
             <entry><literal>%u</literal></entry>
             <entry>User name</entry>
             <entry>yes</entry>
            </row>
            <row>
             <entry><literal>%d</literal></entry>
             <entry>Database name</entry>
             <entry>yes</entry>
            </row>
            <row>
             <entry><literal>%r</literal></entry>
             <entry>Remote host name or IP address, and remote port</entry>
             <entry>yes</entry>
            </row>
            <row>
             <entry><literal>%h</literal></entry>
             <entry>Remote host name or IP address</entry>
             <entry>yes</entry>
            </row>
            <row>
             <entry><literal>%p</literal></entry>
             <entry>Process ID</entry>
             <entry>no</entry>
            </row>
            <row>
             <entry><literal>%t</literal></entry>
             <entry>Time stamp without milliseconds</entry>
             <entry>no</entry>
            </row>
            <row>
             <entry><literal>%m</literal></entry>
             <entry>Time stamp with milliseconds</entry>
             <entry>no</entry>
            </row>
            <row>
             <entry><literal>%n</literal></entry>
             <entry>Time stamp with milliseconds (as a Unix epoch)</entry>
             <entry>no</entry>
            </row>
            <row>
             <entry><literal>%i</literal></entry>
             <entry>Command tag: type of session's current command</entry>
             <entry>yes</entry>
            </row>
            <row>
             <entry><literal>%e</literal></entry>
             <entry>SQLSTATE error code</entry>
             <entry>no</entry>
            </row>
            <row>
             <entry><literal>%c</literal></entry>
             <entry>Session ID: see below</entry>
             <entry>no</entry>
            </row>
            <row>
             <entry><literal>%l</literal></entry>
             <entry>Number of the log line for each session or process, starting at 1</entry>
             <entry>no</entry>
            </row>
            <row>
             <entry><literal>%s</literal></entry>
             <entry>Process start time stamp</entry>
             <entry>no</entry>
            </row>
            <row>
             <entry><literal>%v</literal></entry>
             <entry>Virtual transaction ID (backendID/localXID)</entry>
             <entry>no</entry>
            </row>
            <row>
             <entry><literal>%x</literal></entry>
             <entry>Transaction ID (0 if none is assigned)</entry>
             <entry>no</entry>
            </row>
            <row>
             <entry><literal>%q</literal></entry>
             <entry>Produces no output, but tells non-session
             processes to stop at this point in the string; ignored by
             session processes</entry>
             <entry>no</entry>
            </row>
            <row>
             <entry><literal>%%</literal></entry>
             <entry>Literal <literal>%</></entry>
             <entry>no</entry>
            </row>
           </tbody>
          </tgroup>
         </informaltable>

         The <literal>%c</> escape prints a quasi-unique session identifier,
         consisting of two 4-byte hexadecimal numbers (without leading zeros)
         separated by a dot.  The numbers are the process start time and the
         process ID, so <literal>%c</> can also be used as a space saving way
         of printing those items.  For example, to generate the session
         identifier from <literal>pg_stat_activity</>, use this query:
<programlisting>
SELECT to_hex(trunc(EXTRACT(EPOCH FROM backend_start))::integer) || '.' ||
       to_hex(pid)
FROM pg_stat_activity;
</programlisting>

       </para>

       <tip>
        <para>
         If you set a nonempty value for <varname>log_line_prefix</>,
         you should usually make its last character be a space, to provide
         visual separation from the rest of the log line.  A punctuation
         character can be used too.
        </para>
       </tip>

       <tip>
        <para>
         <application>Syslog</> produces its own
         time stamp and process ID information, so you probably do not want to
         include those escapes if you are logging to <application>syslog</>.
        </para>
       </tip>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-log-lock-waits" xreflabel="log_lock_waits">
      <term><varname>log_lock_waits</varname> (<type>boolean</type>)
      <indexterm>
       <primary><varname>log_lock_waits</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Controls whether a log message is produced when a session waits
        longer than <xref linkend="guc-deadlock-timeout"> to acquire a
        lock.  This is useful in determining if lock waits are causing
        poor performance.  The default is <literal>off</>.
        Only superusers can change this setting.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-log-statement" xreflabel="log_statement">
      <term><varname>log_statement</varname> (<type>enum</type>)
      <indexterm>
       <primary><varname>log_statement</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Controls which SQL statements are logged. Valid values are
        <literal>none</> (off), <literal>ddl</>, <literal>mod</>, and
        <literal>all</> (all statements). <literal>ddl</> logs all data definition
        statements, such as <command>CREATE</>, <command>ALTER</>, and
        <command>DROP</> statements. <literal>mod</> logs all
        <literal>ddl</> statements, plus data-modifying statements
        such as <command>INSERT</>,
        <command>UPDATE</>, <command>DELETE</>, <command>TRUNCATE</>,
        and <command>COPY FROM</>.
        <command>PREPARE</>, <command>EXECUTE</>, and
        <command>EXPLAIN ANALYZE</> statements are also logged if their
        contained command is of an appropriate type.  For clients using
        extended query protocol, logging occurs when an Execute message
        is received, and values of the Bind parameters are included
        (with any embedded single-quote marks doubled).
       </para>

       <para>
        The default is <literal>none</>. Only superusers can change this
        setting.
       </para>

       <note>
        <para>
         Statements that contain simple syntax errors are not logged
         even by the <varname>log_statement</> = <literal>all</> setting,
         because the log message is emitted only after basic parsing has
         been done to determine the statement type.  In the case of extended
         query protocol, this setting likewise does not log statements that
         fail before the Execute phase (i.e., during parse analysis or
         planning).  Set <varname>log_min_error_statement</> to
         <literal>ERROR</> (or lower) to log such statements.
        </para>
       </note>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-log-replication-commands" xreflabel="log_replication_commands">
      <term><varname>log_replication_commands</varname> (<type>boolean</type>)
      <indexterm>
       <primary><varname>log_replication_commands</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Causes each replication command to be logged in the server log.
        See <xref linkend="protocol-replication"> for more information about
        replication command. The default value is <literal>off</>.
        Only superusers can change this setting.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-log-temp-files" xreflabel="log_temp_files">
      <term><varname>log_temp_files</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>log_temp_files</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Controls logging of temporary file names and sizes.
        Temporary files can be
        created for sorts, hashes, and temporary query results.
        A log entry is made for each temporary file when it is deleted.
        A value of zero logs all temporary file information, while positive
        values log only files whose size is greater than or equal to
        the specified number of kilobytes.  The
        default setting is -1, which disables such logging.
        Only superusers can change this setting.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-log-timezone" xreflabel="log_timezone">
      <term><varname>log_timezone</varname> (<type>string</type>)
      <indexterm>
       <primary><varname>log_timezone</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Sets the time zone used for timestamps written in the server log.
        Unlike <xref linkend="guc-timezone">, this value is cluster-wide,
        so that all sessions will report timestamps consistently.
        The built-in default is <literal>GMT</>, but that is typically
        overridden in <filename>postgresql.conf</>; <application>initdb</>
        will install a setting there corresponding to its system environment.
        See <xref linkend="datatype-timezones"> for more information.
        This parameter can only be set in the <filename>postgresql.conf</>
        file or on the server command line.
       </para>
      </listitem>
     </varlistentry>

     </variablelist>
    </sect2>
     <sect2 id="runtime-config-logging-csvlog">
     <title>Using CSV-Format Log Output</title>

       <para>
        Including <literal>csvlog</> in the <varname>log_destination</> list
        provides a convenient way to import log files into a database table.
        This option emits log lines in comma-separated-values
        (<acronym>CSV</>) format,
        with these columns:
        time stamp with milliseconds,
        user name,
        database name,
        process ID,
        client host:port number,
        session ID,
        per-session line number,
        command tag,
        session start time,
        virtual transaction ID,
        regular transaction ID,
        error severity,
        SQLSTATE code,
        error message,
        error message detail,
        hint,
        internal query that led to the error (if any),
        character count of the error position therein,
        error context,
        user query that led to the error (if any and enabled by
        <varname>log_min_error_statement</>),
        character count of the error position therein,
        location of the error in the PostgreSQL source code
        (if <varname>log_error_verbosity</> is set to <literal>verbose</>),
        and application name.
        Here is a sample table definition for storing CSV-format log output:

<programlisting>
CREATE TABLE postgres_log
(
  log_time timestamp(3) with time zone,
  user_name text,
  database_name text,
  process_id integer,
  connection_from text,
  session_id text,
  session_line_num bigint,
  command_tag text,
  session_start_time timestamp with time zone,
  virtual_transaction_id text,
  transaction_id bigint,
  error_severity text,
  sql_state_code text,
  message text,
  detail text,
  hint text,
  internal_query text,
  internal_query_pos integer,
  context text,
  query text,
  query_pos integer,
  location text,
  application_name text,
  PRIMARY KEY (session_id, session_line_num)
);
</programlisting>
       </para>

       <para>
        To import a log file into this table, use the <command>COPY FROM</>
        command:

<programlisting>
COPY postgres_log FROM '/full/path/to/logfile.csv' WITH csv;
</programlisting>
       </para>

       <para>
       There are a few things you need to do to simplify importing CSV log
       files:

       <orderedlist>
         <listitem>
           <para>
            Set <varname>log_filename</varname> and
            <varname>log_rotation_age</> to provide a consistent,
            predictable naming scheme for your log files.  This lets you
            predict what the file name will be and know when an individual log
            file is complete and therefore ready to be imported.
         </para>
        </listitem>

        <listitem>
           <para>
            Set <varname>log_rotation_size</varname> to 0 to disable
            size-based log rotation, as it makes the log file name difficult
            to predict.
           </para>
        </listitem>

        <listitem>
          <para>
           Set <varname>log_truncate_on_rotation</varname> to <literal>on</> so
           that old log data isn't mixed with the new in the same file.
          </para>
        </listitem>

        <listitem>
          <para>
           The table definition above includes a primary key specification.
           This is useful to protect against accidentally importing the same
           information twice.  The <command>COPY</> command commits all of the
           data it imports at one time, so any error will cause the entire
           import to fail.  If you import a partial log file and later import
           the file again when it is complete, the primary key violation will
           cause the import to fail.  Wait until the log is complete and
           closed before importing.  This procedure will also protect against
           accidentally importing a partial line that hasn't been completely
           written, which would also cause <command>COPY</> to fail.
          </para>
        </listitem>
        </orderedlist>
      </para>
    </sect2>

   <sect2>
    <title>Process Title</title>

    <para>
     These settings control how process titles of server processes are
     modified.  Process titles are typically viewed using programs like
     <application>ps</> or, on Windows, <application>Process Explorer</>.
     See <xref linkend="monitoring-ps"> for details.
    </para>

    <variablelist>
     <varlistentry id="guc-cluster-name" xreflabel="cluster_name">
      <term><varname>cluster_name</varname> (<type>string</type>)
      <indexterm>
       <primary><varname>cluster_name</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Sets the cluster name that appears in the process title for all
        server processes in this cluster. The name can be any string of less
        than <symbol>NAMEDATALEN</> characters (64 characters in a standard
        build). Only printable ASCII characters may be used in the
        <varname>cluster_name</varname> value. Other characters will be
        replaced with question marks (<literal>?</literal>).  No name is shown
        if this parameter is set to the empty string <literal>''</> (which is
        the default). This parameter can only be set at server start.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-update-process-title" xreflabel="update_process_title">
      <term><varname>update_process_title</varname> (<type>boolean</type>)
      <indexterm>
       <primary><varname>update_process_title</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Enables updating of the process title every time a new SQL command
        is received by the server.
        This setting defaults to <literal>on</> on most platforms, but it
        defaults to <literal>off</> on Windows due to that platform's larger
        overhead for updating the process title.
        Only superusers can change this setting.
       </para>
      </listitem>
     </varlistentry>
    </variablelist>
   </sect2>
  </sect1>

   <sect1 id="runtime-config-statistics">
    <title>Run-time Statistics</title>

    <sect2 id="runtime-config-statistics-collector">
     <title>Query and Index Statistics Collector</title>

     <para>
      These parameters control server-wide statistics collection features.
      When statistics collection is enabled, the data that is produced can be
      accessed via the <structname>pg_stat</structname> and
      <structname>pg_statio</structname> family of system views.
      Refer to <xref linkend="monitoring"> for more information.
     </para>

     <variablelist>

     <varlistentry id="guc-track-activities" xreflabel="track_activities">
      <term><varname>track_activities</varname> (<type>boolean</type>)
      <indexterm>
       <primary><varname>track_activities</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Enables the collection of information on the currently
        executing command of each session, along with the time when
        that command began execution. This parameter is on by
        default. Note that even when enabled, this information is not
        visible to all users, only to superusers and the user owning
        the session being reported on, so it should not represent a
        security risk.
        Only superusers can change this setting.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-track-activity-query-size" xreflabel="track_activity_query_size">
      <term><varname>track_activity_query_size</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>track_activity_query_size</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
       Specifies the number of bytes reserved to track the currently
       executing command for each active session, for the
       <structname>pg_stat_activity</>.<structfield>query</> field.
       The default value is 1024. This parameter can only be set at server
       start.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-track-counts" xreflabel="track_counts">
      <term><varname>track_counts</varname> (<type>boolean</type>)
      <indexterm>
       <primary><varname>track_counts</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Enables collection of statistics on database activity.
        This parameter is on by default, because the autovacuum
        daemon needs the collected information.
        Only superusers can change this setting.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-track-io-timing" xreflabel="track_io_timing">
      <term><varname>track_io_timing</varname> (<type>boolean</type>)
      <indexterm>
       <primary><varname>track_io_timing</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Enables timing of database I/O calls.  This parameter is off by
        default, because it will repeatedly query the operating system for
        the current time, which may cause significant overhead on some
        platforms.  You can use the <xref linkend="pgtesttiming"> tool to
        measure the overhead of timing on your system.
        I/O timing information is
        displayed in <xref linkend="pg-stat-database-view">, in the output of
        <xref linkend="sql-explain"> when the <literal>BUFFERS</> option is
        used, and by <xref linkend="pgstatstatements">.  Only superusers can
        change this setting.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-track-functions" xreflabel="track_functions">
      <term><varname>track_functions</varname> (<type>enum</type>)
      <indexterm>
       <primary><varname>track_functions</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Enables tracking of function call counts and time used. Specify
        <literal>pl</literal> to track only procedural-language functions,
        <literal>all</literal> to also track SQL and C language functions.
        The default is <literal>none</literal>, which disables function
        statistics tracking.  Only superusers can change this setting.
       </para>

       <note>
        <para>
         SQL-language functions that are simple enough to be <quote>inlined</>
         into the calling query will not be tracked, regardless of this
         setting.
        </para>
       </note>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-stats-temp-directory" xreflabel="stats_temp_directory">
      <term><varname>stats_temp_directory</varname> (<type>string</type>)
      <indexterm>
       <primary><varname>stats_temp_directory</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Sets the directory to store temporary statistics data in. This can be
        a path relative to the data directory or an absolute path. The default
        is <filename>pg_stat_tmp</filename>. Pointing this at a RAM-based
        file system will decrease physical I/O requirements and can lead to
        improved performance.
        This parameter can only be set in the <filename>postgresql.conf</>
        file or on the server command line.
       </para>
      </listitem>
     </varlistentry>

     </variablelist>
    </sect2>

    <sect2 id="runtime-config-statistics-monitor">
     <title>Statistics Monitoring</title>
     <variablelist>

     <varlistentry>
      <term><varname>log_statement_stats</varname> (<type>boolean</type>)
      <indexterm>
       <primary><varname>log_statement_stats</> configuration parameter</primary>
      </indexterm>
      </term>
      <term><varname>log_parser_stats</varname> (<type>boolean</type>)
      <indexterm>
       <primary><varname>log_parser_stats</> configuration parameter</primary>
      </indexterm>
      </term>
      <term><varname>log_planner_stats</varname> (<type>boolean</type>)
      <indexterm>
       <primary><varname>log_planner_stats</> configuration parameter</primary>
      </indexterm>
      </term>
      <term><varname>log_executor_stats</varname> (<type>boolean</type>)
      <indexterm>
       <primary><varname>log_executor_stats</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        For each query, output performance statistics of the respective
        module to the server log. This is a crude profiling
        instrument, similar to the Unix <function>getrusage()</> operating
        system facility.  <varname>log_statement_stats</varname> reports total
        statement statistics, while the others report per-module statistics.
        <varname>log_statement_stats</varname> cannot be enabled together with
        any of the per-module options.  All of these options are disabled by
        default.   Only superusers can change these settings.
       </para>
      </listitem>
     </varlistentry>

     </variablelist>

    </sect2>
   </sect1>

   <sect1 id="runtime-config-autovacuum">
    <title>Automatic Vacuuming</title>

    <indexterm>
     <primary>autovacuum</primary>
     <secondary>configuration parameters</secondary>
    </indexterm>

     <para>
      These settings control the behavior of the <firstterm>autovacuum</>
      feature.  Refer to <xref linkend="autovacuum"> for more information.
      Note that many of these settings can be overridden on a per-table
      basis; see <xref linkend="sql-createtable-storage-parameters"
      endterm="sql-createtable-storage-parameters-title">.
     </para>

    <variablelist>

     <varlistentry id="guc-autovacuum" xreflabel="autovacuum">
      <term><varname>autovacuum</varname> (<type>boolean</type>)
      <indexterm>
       <primary><varname>autovacuum</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Controls whether the server should run the
        autovacuum launcher daemon.  This is on by default; however,
        <xref linkend="guc-track-counts"> must also be enabled for
        autovacuum to work.
        This parameter can only be set in the <filename>postgresql.conf</>
        file or on the server command line; however, autovacuuming can be
        disabled for individual tables by changing table storage parameters.
       </para>
       <para>
        Note that even when this parameter is disabled, the system
        will launch autovacuum processes if necessary to
        prevent transaction ID wraparound.  See <xref
        linkend="vacuum-for-wraparound"> for more information.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-log-autovacuum-min-duration" xreflabel="log_autovacuum_min_duration">
      <term><varname>log_autovacuum_min_duration</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>log_autovacuum_min_duration</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Causes each action executed by autovacuum to be logged if it ran for at
        least the specified number of milliseconds.  Setting this to zero logs
        all autovacuum actions. Minus-one (the default) disables logging
        autovacuum actions.  For example, if you set this to
        <literal>250ms</literal> then all automatic vacuums and analyzes that run
        250ms or longer will be logged.  In addition, when this parameter is
        set to any value other than <literal>-1</literal>, a message will be
        logged if an autovacuum action is skipped due to the existence of a
        conflicting lock.  Enabling this parameter can be helpful
        in tracking autovacuum activity.  This parameter can only be set in
        the <filename>postgresql.conf</> file or on the server command line;
        but the setting can be overridden for individual tables by
        changing table storage parameters.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-autovacuum-max-workers" xreflabel="autovacuum_max_workers">
      <term><varname>autovacuum_max_workers</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>autovacuum_max_workers</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Specifies the maximum number of autovacuum processes (other than the
        autovacuum launcher) that may be running at any one time.  The default
        is three.  This parameter can only be set at server start.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-autovacuum-naptime" xreflabel="autovacuum_naptime">
      <term><varname>autovacuum_naptime</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>autovacuum_naptime</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Specifies the minimum delay between autovacuum runs on any given
        database.  In each round the daemon examines the
        database and issues <command>VACUUM</> and <command>ANALYZE</> commands
        as needed for tables in that database.  The delay is measured
        in seconds, and the default is one minute (<literal>1min</>).
        This parameter can only be set in the <filename>postgresql.conf</>
        file or on the server command line.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-autovacuum-vacuum-threshold" xreflabel="autovacuum_vacuum_threshold">
      <term><varname>autovacuum_vacuum_threshold</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>autovacuum_vacuum_threshold</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Specifies the minimum number of updated or deleted tuples needed
        to trigger a <command>VACUUM</> in any one table.
        The default is 50 tuples.
        This parameter can only be set in the <filename>postgresql.conf</>
        file or on the server command line;
        but the setting can be overridden for individual tables by
        changing table storage parameters.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-autovacuum-analyze-threshold" xreflabel="autovacuum_analyze_threshold">
      <term><varname>autovacuum_analyze_threshold</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>autovacuum_analyze_threshold</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Specifies the minimum number of inserted, updated or deleted tuples
        needed to trigger an <command>ANALYZE</> in any one table.
        The default is 50 tuples.
        This parameter can only be set in the <filename>postgresql.conf</>
        file or on the server command line;
        but the setting can be overridden for individual tables by
        changing table storage parameters.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-autovacuum-vacuum-scale-factor" xreflabel="autovacuum_vacuum_scale_factor">
      <term><varname>autovacuum_vacuum_scale_factor</varname> (<type>floating point</type>)
      <indexterm>
       <primary><varname>autovacuum_vacuum_scale_factor</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Specifies a fraction of the table size to add to
        <varname>autovacuum_vacuum_threshold</varname>
        when deciding whether to trigger a <command>VACUUM</>.
        The default is 0.2 (20% of table size).
        This parameter can only be set in the <filename>postgresql.conf</>
        file or on the server command line;
        but the setting can be overridden for individual tables by
        changing table storage parameters.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-autovacuum-analyze-scale-factor" xreflabel="autovacuum_analyze_scale_factor">
      <term><varname>autovacuum_analyze_scale_factor</varname> (<type>floating point</type>)
      <indexterm>
       <primary><varname>autovacuum_analyze_scale_factor</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Specifies a fraction of the table size to add to
        <varname>autovacuum_analyze_threshold</varname>
        when deciding whether to trigger an <command>ANALYZE</>.
        The default is 0.1 (10% of table size).
        This parameter can only be set in the <filename>postgresql.conf</>
        file or on the server command line;
        but the setting can be overridden for individual tables by
        changing table storage parameters.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-autovacuum-freeze-max-age" xreflabel="autovacuum_freeze_max_age">
      <term><varname>autovacuum_freeze_max_age</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>autovacuum_freeze_max_age</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Specifies the maximum age (in transactions) that a table's
        <structname>pg_class</>.<structfield>relfrozenxid</> field can
        attain before a <command>VACUUM</> operation is forced
        to prevent transaction ID wraparound within the table.
        Note that the system will launch autovacuum processes to
        prevent wraparound even when autovacuum is otherwise disabled.
       </para>

       <para>
        Vacuum also allows removal of old files from the
        <filename>pg_clog</> subdirectory, which is why the default
        is a relatively low 200 million transactions.
        This parameter can only be set at server start, but the setting
        can be reduced for individual tables by
        changing table storage parameters.
        For more information see <xref linkend="vacuum-for-wraparound">.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-autovacuum-multixact-freeze-max-age" xreflabel="autovacuum_multixact_freeze_max_age">
      <term><varname>autovacuum_multixact_freeze_max_age</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>autovacuum_multixact_freeze_max_age</varname> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Specifies the maximum age (in multixacts) that a table's
        <structname>pg_class</>.<structfield>relminmxid</> field can
        attain before a <command>VACUUM</> operation is forced to
        prevent multixact ID wraparound within the table.
        Note that the system will launch autovacuum processes to
        prevent wraparound even when autovacuum is otherwise disabled.
       </para>

       <para>
        Vacuuming multixacts also allows removal of old files from the
        <filename>pg_multixact/members</> and <filename>pg_multixact/offsets</>
        subdirectories, which is why the default is a relatively low
        400 million multixacts.
        This parameter can only be set at server start, but the setting can
        be reduced for individual tables by changing table storage parameters.
        For more information see <xref linkend="vacuum-for-multixact-wraparound">.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-autovacuum-vacuum-cost-delay" xreflabel="autovacuum_vacuum_cost_delay">
      <term><varname>autovacuum_vacuum_cost_delay</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>autovacuum_vacuum_cost_delay</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Specifies the cost delay value that will be used in automatic
        <command>VACUUM</> operations.  If -1 is specified, the regular
        <xref linkend="guc-vacuum-cost-delay"> value will be used.
        The default value is 20 milliseconds.
        This parameter can only be set in the <filename>postgresql.conf</>
        file or on the server command line;
        but the setting can be overridden for individual tables by
        changing table storage parameters.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-autovacuum-vacuum-cost-limit" xreflabel="autovacuum_vacuum_cost_limit">
      <term><varname>autovacuum_vacuum_cost_limit</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>autovacuum_vacuum_cost_limit</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Specifies the cost limit value that will be used in automatic
        <command>VACUUM</> operations.  If -1 is specified (which is the
        default), the regular
        <xref linkend="guc-vacuum-cost-limit"> value will be used.  Note that
        the value is distributed proportionally among the running autovacuum
        workers, if there is more than one, so that the sum of the limits for
        each worker does not exceed the value of this variable.
        This parameter can only be set in the <filename>postgresql.conf</>
        file or on the server command line;
        but the setting can be overridden for individual tables by
        changing table storage parameters.
       </para>
      </listitem>
     </varlistentry>

    </variablelist>
   </sect1>

   <sect1 id="runtime-config-client">
    <title>Client Connection Defaults</title>

    <sect2 id="runtime-config-client-statement">
     <title>Statement Behavior</title>
     <variablelist>

     <varlistentry id="guc-search-path" xreflabel="search_path">
      <term><varname>search_path</varname> (<type>string</type>)
      <indexterm>
       <primary><varname>search_path</> configuration parameter</primary>
      </indexterm>
      <indexterm><primary>path</><secondary>for schemas</></>
      </term>
      <listitem>
       <para>
        This variable specifies the order in which schemas are searched
        when an object (table, data type, function, etc.) is referenced by a
        simple name with no schema specified.  When there are objects of
        identical names in different schemas, the one found first
        in the search path is used.  An object that is not in any of the
        schemas in the search path can only be referenced by specifying
        its containing schema with a qualified (dotted) name.
       </para>

       <para>
        The value for <varname>search_path</varname> must be a comma-separated
        list of schema names.  Any name that is not an existing schema, or is
        a schema for which the user does not have <literal>USAGE</>
        permission, is silently ignored.
       </para>

       <para>
        If one of the list items is the special name
        <literal>$user</literal>, then the schema having the name returned by
        <function>CURRENT_USER</> is substituted, if there is such a schema
        and the user has <literal>USAGE</> permission for it.
        (If not, <literal>$user</literal> is ignored.)
       </para>

       <para>
        The system catalog schema, <literal>pg_catalog</>, is always
        searched, whether it is mentioned in the path or not.  If it is
        mentioned in the path then it will be searched in the specified
        order.  If <literal>pg_catalog</> is not in the path then it will
        be searched <emphasis>before</> searching any of the path items.
       </para>

       <!-- To further split hairs, funcname('foo') does not use the temporary
            schema, even when it considers typname='funcname'.  This paragraph
            refers to function names in a loose sense, "pg_proc.proname or
            func_name grammar production". -->
       <para>
        Likewise, the current session's temporary-table schema,
        <literal>pg_temp_<replaceable>nnn</></>, is always searched if it
        exists.  It can be explicitly listed in the path by using the
        alias <literal>pg_temp</><indexterm><primary>pg_temp</></>.  If it is not listed in the path then
        it is searched first (even before <literal>pg_catalog</>).  However,
        the temporary schema is only searched for relation (table, view,
        sequence, etc) and data type names.  It is never searched for
        function or operator names.
       </para>

       <para>
        When objects are created without specifying a particular target
        schema, they will be placed in the first valid schema named in
        <varname>search_path</varname>.  An error is reported if the search
        path is empty.
       </para>

       <para>
        The default value for this parameter is
        <literal>"$user", public</literal>.
        This setting supports shared use of a database (where no users
        have private schemas, and all share use of <literal>public</>),
        private per-user schemas, and combinations of these.  Other
        effects can be obtained by altering the default search path
        setting, either globally or per-user.
       </para>

       <para>
        For more information on schema handling, see
        <xref linkend="ddl-schemas">.  In particular, the default
        configuration is suitable only when the database has a single user or
        a few mutually-trusting users.
       </para>

       <para>
        The current effective value of the search path can be examined
        via the <acronym>SQL</acronym> function
        <function>current_schemas</>
        (see <xref linkend="functions-info">).
        This is not quite the same as
        examining the value of <varname>search_path</varname>, since
        <function>current_schemas</> shows how the items
        appearing in <varname>search_path</varname> were resolved.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-row-security" xreflabel="row_security">
      <term><varname>row_security</varname> (<type>boolean</type>)
      <indexterm>
       <primary><varname>row_security</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        This variable controls whether to raise an error in lieu of applying a
        row security policy.  When set to <literal>on</>, policies apply
        normally.  When set to <literal>off</>, queries fail which would
        otherwise apply at least one policy.  The default is <literal>on</>.
        Change to <literal>off</> where limited row visibility could cause
        incorrect results; for example, <application>pg_dump</> makes that
        change by default.  This variable has no effect on roles which bypass
        every row security policy, to wit, superusers and roles with
        the <literal>BYPASSRLS</> attribute.
       </para>

       <para>
        For more information on row security policies,
        see <xref linkend="SQL-CREATEPOLICY">.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-default-tablespace" xreflabel="default_tablespace">
      <term><varname>default_tablespace</varname> (<type>string</type>)
      <indexterm>
       <primary><varname>default_tablespace</> configuration parameter</primary>
      </indexterm>
      <indexterm><primary>tablespace</><secondary>default</></>
      </term>
      <listitem>
       <para>
        This variable specifies the default tablespace in which to create
        objects (tables and indexes) when a <command>CREATE</> command does
        not explicitly specify a tablespace.
       </para>

       <para>
        The value is either the name of a tablespace, or an empty string
        to specify using the default tablespace of the current database.
        If the value does not match the name of any existing tablespace,
        <productname>PostgreSQL</> will automatically use the default
        tablespace of the current database.  If a nondefault tablespace
        is specified, the user must have <literal>CREATE</> privilege
        for it, or creation attempts will fail.
       </para>

       <para>
        This variable is not used for temporary tables; for them,
        <xref linkend="guc-temp-tablespaces"> is consulted instead.
       </para>

       <para>
        This variable is also not used when creating databases.
        By default, a new database inherits its tablespace setting from
        the template database it is copied from.
       </para>

       <para>
        For more information on tablespaces,
        see <xref linkend="manage-ag-tablespaces">.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-temp-tablespaces" xreflabel="temp_tablespaces">
      <term><varname>temp_tablespaces</varname> (<type>string</type>)
      <indexterm>
       <primary><varname>temp_tablespaces</> configuration parameter</primary>
      </indexterm>
      <indexterm><primary>tablespace</><secondary>temporary</></>
      </term>
      <listitem>
       <para>
        This variable specifies tablespaces in which to create temporary
        objects (temp tables and indexes on temp tables) when a
        <command>CREATE</> command does not explicitly specify a tablespace.
        Temporary files for purposes such as sorting large data sets
        are also created in these tablespaces.
       </para>

       <para>
        The value is a list of names of tablespaces.  When there is more than
        one name in the list, <productname>PostgreSQL</> chooses a random
        member of the list each time a temporary object is to be created;
        except that within a transaction, successively created temporary
        objects are placed in successive tablespaces from the list.
        If the selected element of the list is an empty string,
        <productname>PostgreSQL</> will automatically use the default
        tablespace of the current database instead.
       </para>

       <para>
        When <varname>temp_tablespaces</> is set interactively, specifying a
        nonexistent tablespace is an error, as is specifying a tablespace for
        which the user does not have <literal>CREATE</> privilege.  However,
        when using a previously set value, nonexistent tablespaces are
        ignored, as are tablespaces for which the user lacks
        <literal>CREATE</> privilege.  In particular, this rule applies when
        using a value set in <filename>postgresql.conf</>.
       </para>

       <para>
        The default value is an empty string, which results in all temporary
        objects being created in the default tablespace of the current
        database.
       </para>

       <para>
        See also <xref linkend="guc-default-tablespace">.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-check-function-bodies" xreflabel="check_function_bodies">
      <term><varname>check_function_bodies</varname> (<type>boolean</type>)
      <indexterm>
       <primary><varname>check_function_bodies</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        This parameter is normally on. When set to <literal>off</>, it
        disables validation of the function body string during <xref
        linkend="sql-createfunction">.  Disabling validation avoids side
        effects of the validation process and avoids false positives due
        to problems such as forward references.  Set this parameter
        to <literal>off</> before loading functions on behalf of other
        users; <application>pg_dump</> does so automatically.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-default-transaction-isolation" xreflabel="default_transaction_isolation">
      <term><varname>default_transaction_isolation</varname> (<type>enum</type>)
      <indexterm>
       <primary>transaction isolation level</primary>
       <secondary>setting default</secondary>
      </indexterm>
      <indexterm>
       <primary><varname>default_transaction_isolation</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Each SQL transaction has an isolation level, which can be
        either <quote>read uncommitted</quote>, <quote>read
        committed</quote>, <quote>repeatable read</quote>, or
        <quote>serializable</quote>.  This parameter controls the
        default isolation level of each new transaction. The default
        is <quote>read committed</quote>.
       </para>

       <para>
        Consult <xref linkend="mvcc"> and <xref
        linkend="sql-set-transaction"> for more information.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-default-transaction-read-only" xreflabel="default_transaction_read_only">
      <term><varname>default_transaction_read_only</varname> (<type>boolean</type>)
      <indexterm>
       <primary>read-only transaction</primary>
       <secondary>setting default</secondary>
      </indexterm>
      <indexterm>
       <primary><varname>default_transaction_read_only</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        A read-only SQL transaction cannot alter non-temporary tables.
        This parameter controls the default read-only status of each new
        transaction. The default is <literal>off</> (read/write).
       </para>

       <para>
        Consult <xref linkend="sql-set-transaction"> for more information.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-default-transaction-deferrable" xreflabel="default_transaction_deferrable">
      <term><varname>default_transaction_deferrable</varname> (<type>boolean</type>)
      <indexterm>
       <primary>deferrable transaction</primary>
       <secondary>setting default</secondary>
      </indexterm>
      <indexterm>
       <primary><varname>default_transaction_deferrable</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        When running at the <literal>serializable</> isolation level,
        a deferrable read-only SQL transaction may be delayed before
        it is allowed to proceed.  However, once it begins executing
        it does not incur any of the overhead required to ensure
        serializability; so serialization code will have no reason to
        force it to abort because of concurrent updates, making this
        option suitable for long-running read-only transactions.
        </para>

        <para>
        This parameter controls the default deferrable status of each
        new transaction.  It currently has no effect on read-write
        transactions or those operating at isolation levels lower
        than <literal>serializable</>. The default is <literal>off</>.
       </para>

       <para>
        Consult <xref linkend="sql-set-transaction"> for more information.
       </para>
      </listitem>
     </varlistentry>


     <varlistentry id="guc-session-replication-role" xreflabel="session_replication_role">
      <term><varname>session_replication_role</varname> (<type>enum</type>)
      <indexterm>
       <primary><varname>session_replication_role</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Controls firing of replication-related triggers and rules for the
        current session.  Setting this variable requires
        superuser privilege and results in discarding any previously cached
        query plans.  Possible values are <literal>origin</> (the default),
        <literal>replica</> and <literal>local</>.
        See <xref linkend="sql-altertable"> for
        more information.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-statement-timeout" xreflabel="statement_timeout">
      <term><varname>statement_timeout</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>statement_timeout</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Abort any statement that takes more than the specified number of
        milliseconds, starting from the time the command arrives at the server
        from the client.  If <varname>log_min_error_statement</> is set to
        <literal>ERROR</> or lower, the statement that timed out will also be
        logged.  A value of zero (the default) turns this off.
       </para>

       <para>
        Setting <varname>statement_timeout</> in
        <filename>postgresql.conf</> is not recommended because it would
        affect all sessions.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-lock-timeout" xreflabel="lock_timeout">
      <term><varname>lock_timeout</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>lock_timeout</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Abort any statement that waits longer than the specified number of
        milliseconds while attempting to acquire a lock on a table, index,
        row, or other database object.  The time limit applies separately to
        each lock acquisition attempt.  The limit applies both to explicit
        locking requests (such as <command>LOCK TABLE</>, or <command>SELECT
        FOR UPDATE</> without <literal>NOWAIT</>) and to implicitly-acquired
        locks.  If <varname>log_min_error_statement</> is set to
        <literal>ERROR</> or lower, the statement that timed out will be
        logged.  A value of zero (the default) turns this off.
       </para>

       <para>
        Unlike <varname>statement_timeout</>, this timeout can only occur
        while waiting for locks.  Note that if <varname>statement_timeout</>
        is nonzero, it is rather pointless to set <varname>lock_timeout</> to
        the same or larger value, since the statement timeout would always
        trigger first.
       </para>

       <para>
        Setting <varname>lock_timeout</> in
        <filename>postgresql.conf</> is not recommended because it would
        affect all sessions.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-idle-in-transaction-session-timeout" xreflabel="idle_in_transaction_session_timeout">
      <term><varname>idle_in_transaction_session_timeout</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>idle_in_transaction_session_timeout</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
       Terminate any session with an open transaction that has been idle for
       longer than the specified duration in milliseconds. This allows any
       locks held by that session to be released and the connection slot to be reused;
       it also allows tuples visible only to this transaction to be vacuumed.  See
       <xref linkend="routine-vacuuming"> for more details about this.
       </para>
       <para>
       The default value of 0 disables this feature.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-vacuum-freeze-table-age" xreflabel="vacuum_freeze_table_age">
      <term><varname>vacuum_freeze_table_age</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>vacuum_freeze_table_age</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        <command>VACUUM</> performs an aggressive scan if the table's
        <structname>pg_class</>.<structfield>relfrozenxid</> field has reached
        the age specified by this setting.  An aggressive scan differs from
        a regular <command>VACUUM</> in that it visits every page that might
        contain unfrozen XIDs or MXIDs, not just those that might contain dead
        tuples.  The default is 150 million transactions.  Although users can
        set this value anywhere from zero to two billions, <command>VACUUM</>
        will silently limit the effective value to 95% of
        <xref linkend="guc-autovacuum-freeze-max-age">, so that a
        periodical manual <command>VACUUM</> has a chance to run before an
        anti-wraparound autovacuum is launched for the table. For more
        information see
        <xref linkend="vacuum-for-wraparound">.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-vacuum-freeze-min-age" xreflabel="vacuum_freeze_min_age">
      <term><varname>vacuum_freeze_min_age</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>vacuum_freeze_min_age</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Specifies the cutoff age (in transactions) that <command>VACUUM</>
        should use to decide whether to freeze row versions
        while scanning a table.
        The default is 50 million transactions.  Although
        users can set this value anywhere from zero to one billion,
        <command>VACUUM</> will silently limit the effective value to half
        the value of <xref linkend="guc-autovacuum-freeze-max-age">, so
        that there is not an unreasonably short time between forced
        autovacuums.  For more information see <xref
        linkend="vacuum-for-wraparound">.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-vacuum-multixact-freeze-table-age" xreflabel="vacuum_multixact_freeze_table_age">
      <term><varname>vacuum_multixact_freeze_table_age</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>vacuum_multixact_freeze_table_age</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        <command>VACUUM</> performs an aggressive scan if the table's
        <structname>pg_class</>.<structfield>relminmxid</> field has reached
        the age specified by this setting.  An aggressive scan differs from
        a regular <command>VACUUM</> in that it visits every page that might
        contain unfrozen XIDs or MXIDs, not just those that might contain dead
        tuples.  The default is 150 million multixacts.
        Although users can set this value anywhere from zero to two billions,
        <command>VACUUM</> will silently limit the effective value to 95% of
        <xref linkend="guc-autovacuum-multixact-freeze-max-age">, so that a
        periodical manual <command>VACUUM</> has a chance to run before an
        anti-wraparound is launched for the table.
        For more information see <xref linkend="vacuum-for-multixact-wraparound">.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-vacuum-multixact-freeze-min-age" xreflabel="vacuum_multixact_freeze_min_age">
      <term><varname>vacuum_multixact_freeze_min_age</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>vacuum_multixact_freeze_min_age</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Specifies the cutoff age (in multixacts) that <command>VACUUM</>
        should use to decide whether to replace multixact IDs with a newer
        transaction ID or multixact ID while scanning a table.  The default
        is 5 million multixacts.
        Although users can set this value anywhere from zero to one billion,
        <command>VACUUM</> will silently limit the effective value to half
        the value of <xref linkend="guc-autovacuum-multixact-freeze-max-age">,
        so that there is not an unreasonably short time between forced
        autovacuums.
        For more information see <xref linkend="vacuum-for-multixact-wraparound">.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-bytea-output" xreflabel="bytea_output">
      <term><varname>bytea_output</varname> (<type>enum</type>)
      <indexterm>
       <primary><varname>bytea_output</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Sets the output format for values of type <type>bytea</type>.
        Valid values are <literal>hex</literal> (the default)
        and <literal>escape</literal> (the traditional PostgreSQL
        format).  See <xref linkend="datatype-binary"> for more
        information.  The <type>bytea</type> type always
        accepts both formats on input, regardless of this setting.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-xmlbinary" xreflabel="xmlbinary">
      <term><varname>xmlbinary</varname> (<type>enum</type>)
      <indexterm>
       <primary><varname>xmlbinary</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Sets how binary values are to be encoded in XML.  This applies
        for example when <type>bytea</type> values are converted to
        XML by the functions <function>xmlelement</function> or
        <function>xmlforest</function>.  Possible values are
        <literal>base64</literal> and <literal>hex</literal>, which
        are both defined in the XML Schema standard.  The default is
        <literal>base64</literal>.  For further information about
        XML-related functions, see <xref linkend="functions-xml">.
       </para>

       <para>
        The actual choice here is mostly a matter of taste,
        constrained only by possible restrictions in client
        applications.  Both methods support all possible values,
        although the hex encoding will be somewhat larger than the
        base64 encoding.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-xmloption" xreflabel="xmloption">
      <term><varname>xmloption</varname> (<type>enum</type>)
      <indexterm>
       <primary><varname>xmloption</> configuration parameter</primary>
      </indexterm>
      <indexterm>
       <primary><varname>SET XML OPTION</></primary>
      </indexterm>
      <indexterm>
       <primary>XML option</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Sets whether <literal>DOCUMENT</literal> or
        <literal>CONTENT</literal> is implicit when converting between
        XML and character string values.  See <xref
        linkend="datatype-xml"> for a description of this.  Valid
        values are <literal>DOCUMENT</literal> and
        <literal>CONTENT</literal>.  The default is
        <literal>CONTENT</literal>.
       </para>

       <para>
        According to the SQL standard, the command to set this option is
<synopsis>
SET XML OPTION { DOCUMENT | CONTENT };
</synopsis>
        This syntax is also available in PostgreSQL.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-gin-pending-list-limit" xreflabel="gin_pending_list_limit">
      <term><varname>gin_pending_list_limit</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>gin_pending_list_limit</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Sets the maximum size of the GIN pending list which is used
        when <literal>fastupdate</> is enabled. If the list grows
        larger than this maximum size, it is cleaned up by moving
        the entries in it to the main GIN data structure in bulk.
        The default is four megabytes (<literal>4MB</>). This setting
        can be overridden for individual GIN indexes by changing
        index storage parameters.
         See <xref linkend="gin-fast-update"> and <xref linkend="gin-tips">
         for more information.
       </para>
      </listitem>
     </varlistentry>

     </variablelist>
    </sect2>
     <sect2 id="runtime-config-client-format">
     <title>Locale and Formatting</title>

     <variablelist>

     <varlistentry id="guc-datestyle" xreflabel="DateStyle">
      <term><varname>DateStyle</varname> (<type>string</type>)
      <indexterm>
       <primary><varname>DateStyle</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Sets the display format for date and time values, as well as the
        rules for interpreting ambiguous date input values. For
        historical reasons, this variable contains two independent
        components: the output format specification (<literal>ISO</>,
        <literal>Postgres</>, <literal>SQL</>, or <literal>German</>)
        and the input/output specification for year/month/day ordering
        (<literal>DMY</>, <literal>MDY</>, or <literal>YMD</>). These
        can be set separately or together. The keywords <literal>Euro</>
        and <literal>European</> are synonyms for <literal>DMY</>; the
        keywords <literal>US</>, <literal>NonEuro</>, and
        <literal>NonEuropean</> are synonyms for <literal>MDY</>. See
        <xref linkend="datatype-datetime"> for more information. The
        built-in default is <literal>ISO, MDY</>, but
        <application>initdb</application> will initialize the
        configuration file with a setting that corresponds to the
        behavior of the chosen <varname>lc_time</varname> locale.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-intervalstyle" xreflabel="IntervalStyle">
      <term><varname>IntervalStyle</varname> (<type>enum</type>)
      <indexterm>
       <primary><varname>IntervalStyle</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Sets the display format for interval values.
        The value <literal>sql_standard</> will produce
        output matching <acronym>SQL</acronym> standard interval literals.
        The value <literal>postgres</> (which is the default) will produce
        output matching <productname>PostgreSQL</> releases prior to 8.4
        when the <xref linkend="guc-datestyle">
        parameter was set to <literal>ISO</>.
        The value <literal>postgres_verbose</> will produce output
        matching <productname>PostgreSQL</> releases prior to 8.4
        when the <varname>DateStyle</>
        parameter was set to non-<literal>ISO</> output.
        The value <literal>iso_8601</> will produce output matching the time
        interval <quote>format with designators</> defined in section
        4.4.3.2 of ISO 8601.
       </para>
       <para>
        The <varname>IntervalStyle</> parameter also affects the
        interpretation of ambiguous interval input.  See
        <xref linkend="datatype-interval-input"> for more information.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-timezone" xreflabel="TimeZone">
      <term><varname>TimeZone</varname> (<type>string</type>)
      <indexterm>
       <primary><varname>TimeZone</> configuration parameter</primary>
      </indexterm>
      <indexterm><primary>time zone</></>
      </term>
      <listitem>
       <para>
        Sets the time zone for displaying and interpreting time stamps.
        The built-in default is <literal>GMT</>, but that is typically
        overridden in <filename>postgresql.conf</>; <application>initdb</>
        will install a setting there corresponding to its system environment.
        See <xref linkend="datatype-timezones"> for more information.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-timezone-abbreviations" xreflabel="timezone_abbreviations">
      <term><varname>timezone_abbreviations</varname> (<type>string</type>)
      <indexterm>
       <primary><varname>timezone_abbreviations</> configuration parameter</primary>
      </indexterm>
      <indexterm><primary>time zone names</></>
      </term>
      <listitem>
       <para>
        Sets the collection of time zone abbreviations that will be accepted
        by the server for datetime input.  The default is <literal>'Default'</>,
        which is a collection that works in most of the world; there are
        also <literal>'Australia'</literal> and <literal>'India'</literal>,
        and other collections can be defined for a particular installation.
        See <xref linkend="datetime-config-files"> for more information.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-extra-float-digits" xreflabel="extra_float_digits">
      <term><varname>extra_float_digits</varname> (<type>integer</type>)
      <indexterm>
       <primary>significant digits</primary>
      </indexterm>
      <indexterm>
       <primary>floating-point</primary>
       <secondary>display</secondary>
      </indexterm>
      <indexterm>
       <primary><varname>extra_float_digits</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        This parameter adjusts the number of digits displayed for
        floating-point values, including <type>float4</>, <type>float8</>,
        and geometric data types.  The parameter value is added to the
        standard number of digits (<literal>FLT_DIG</> or <literal>DBL_DIG</>
        as appropriate).  The value can be set as high as 3, to include
        partially-significant digits; this is especially useful for dumping
        float data that needs to be restored exactly.  Or it can be set
        negative to suppress unwanted digits.
        See also <xref linkend="datatype-float">.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-client-encoding" xreflabel="client_encoding">
      <term><varname>client_encoding</varname> (<type>string</type>)
      <indexterm>
       <primary><varname>client_encoding</> configuration parameter</primary>
      </indexterm>
      <indexterm><primary>character set</></>
      </term>
      <listitem>
       <para>
        Sets the client-side encoding (character set).
        The default is to use the database encoding.
        The character sets supported by the <productname>PostgreSQL</productname>
        server are described in <xref linkend="multibyte-charset-supported">.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-lc-messages" xreflabel="lc_messages">
      <term><varname>lc_messages</varname> (<type>string</type>)
      <indexterm>
       <primary><varname>lc_messages</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Sets the language in which messages are displayed.  Acceptable
        values are system-dependent; see <xref linkend="locale"> for
        more information.  If this variable is set to the empty string
        (which is the default) then the value is inherited from the
        execution environment of the server in a system-dependent way.
       </para>

       <para>
        On some systems, this locale category does not exist.  Setting
        this variable will still work, but there will be no effect.
        Also, there is a chance that no translated messages for the
        desired language exist.  In that case you will continue to see
        the English messages.
       </para>

       <para>
        Only superusers can change this setting, because it affects the
        messages sent to the server log as well as to the client, and
        an improper value might obscure the readability of the server
        logs.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-lc-monetary" xreflabel="lc_monetary">
      <term><varname>lc_monetary</varname> (<type>string</type>)
      <indexterm>
       <primary><varname>lc_monetary</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Sets the locale to use for formatting monetary amounts, for
        example with the <function>to_char</function> family of
        functions.  Acceptable values are system-dependent; see <xref
        linkend="locale"> for more information.  If this variable is
        set to the empty string (which is the default) then the value
        is inherited from the execution environment of the server in a
        system-dependent way.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-lc-numeric" xreflabel="lc_numeric">
      <term><varname>lc_numeric</varname> (<type>string</type>)
      <indexterm>
       <primary><varname>lc_numeric</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Sets the locale to use for formatting numbers, for example
        with the <function>to_char</function> family of
        functions. Acceptable values are system-dependent; see <xref
        linkend="locale"> for more information.  If this variable is
        set to the empty string (which is the default) then the value
        is inherited from the execution environment of the server in a
        system-dependent way.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-lc-time" xreflabel="lc_time">
      <term><varname>lc_time</varname> (<type>string</type>)
      <indexterm>
       <primary><varname>lc_time</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Sets the locale to use for formatting dates and times, for example
        with the <function>to_char</function> family of
        functions. Acceptable values are system-dependent; see <xref
        linkend="locale"> for more information.  If this variable is
        set to the empty string (which is the default) then the value
        is inherited from the execution environment of the server in a
        system-dependent way.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-default-text-search-config" xreflabel="default_text_search_config">
      <term><varname>default_text_search_config</varname> (<type>string</type>)
      <indexterm>
       <primary><varname>default_text_search_config</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Selects the text search configuration that is used by those variants
        of the text search functions that do not have an explicit argument
        specifying the configuration.
        See <xref linkend="textsearch"> for further information.
        The built-in default is <literal>pg_catalog.simple</>, but
        <application>initdb</application> will initialize the
        configuration file with a setting that corresponds to the
        chosen <varname>lc_ctype</varname> locale, if a configuration
        matching that locale can be identified.
       </para>
      </listitem>
     </varlistentry>

     </variablelist>

    </sect2>

    <sect2 id="runtime-config-client-preload">
     <title>Shared Library Preloading</title>

     <para>
      Several settings are available for preloading shared libraries into the
      server, in order to load additional functionality or achieve performance
      benefits.  For example, a setting of
      <literal>'$libdir/mylib'</literal> would cause
      <literal>mylib.so</> (or on some platforms,
      <literal>mylib.sl</>) to be preloaded from the installation's standard
      library directory.  The differences between the settings are when they
      take effect and what privileges are required to change them.
     </para>

     <para>
      <productname>PostgreSQL</productname> procedural language libraries can
      be preloaded in this way, typically by using the
      syntax <literal>'$libdir/plXXX'</literal> where
      <literal>XXX</literal> is <literal>pgsql</>, <literal>perl</>,
      <literal>tcl</>, or <literal>python</>.
     </para>

     <para>
      For each parameter, if more than one library is to be loaded, separate
      their names with commas.  All library names are converted to lower case
      unless double-quoted.
     </para>

     <para>
      Only shared libraries specifically intended to be used with PostgreSQL
      can be loaded this way.  Every PostgreSQL-supported library has
      a <quote>magic block</> that is checked to guarantee compatibility.  For
      this reason, non-PostgreSQL libraries cannot be loaded in this way.  You
      might be able to use operating-system facilities such
      as <envar>LD_PRELOAD</envar> for that.
     </para>

     <para>
      In general, refer to the documentation of a specific module for the
      recommended way to load that module.
     </para>

     <variablelist>
     <varlistentry id="guc-local-preload-libraries" xreflabel="local_preload_libraries">
      <term><varname>local_preload_libraries</varname> (<type>string</type>)
      <indexterm>
       <primary><varname>local_preload_libraries</> configuration parameter</primary>
      </indexterm>
      <indexterm>
       <primary><filename>$libdir/plugins</></primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        This variable specifies one or more shared libraries that are to be
        preloaded at connection start.
        The parameter value only takes effect at the start of the connection.
        Subsequent changes have no effect.  If a specified library is not
        found, the connection attempt will fail.
       </para>

       <para>
        This option can be set by any user.  Because of that, the libraries
        that can be loaded are restricted to those appearing in the
        <filename>plugins</> subdirectory of the installation's
        standard library directory.  (It is the database administrator's
        responsibility to ensure that only <quote>safe</> libraries
        are installed there.)  Entries in <varname>local_preload_libraries</>
        can specify this directory explicitly, for example
        <literal>$libdir/plugins/mylib</literal>, or just specify
        the library name &mdash; <literal>mylib</literal> would have
        the same effect as <literal>$libdir/plugins/mylib</literal>.
       </para>

       <para>
        The intent of this feature is to allow unprivileged users to load
        debugging or performance-measurement libraries into specific sessions
        without requiring an explicit <command>LOAD</> command.  To that end,
        it would be typical to set this parameter using
        the <envar>PGOPTIONS</envar> environment variable on the client or by
        using
        <command>ALTER ROLE SET</>.
       </para>

       <para>
        However, unless a module is specifically designed to be used in this way by
        non-superusers, this is usually not the right setting to use.  Look
        at <xref linkend="guc-session-preload-libraries"> instead.
       </para>
      </listitem>
     </varlistentry>


     <varlistentry id="guc-session-preload-libraries" xreflabel="session_preload_libraries">
      <term><varname>session_preload_libraries</varname> (<type>string</type>)
      <indexterm>
       <primary><varname>session_preload_libraries</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        This variable specifies one or more shared libraries that are to be
        preloaded at connection start.  Only superusers can change this setting.
        The parameter value only takes effect at the start of the connection.
        Subsequent changes have no effect.  If a specified library is not
        found, the connection attempt will fail.
       </para>

       <para>
        The intent of this feature is to allow debugging or
        performance-measurement libraries to be loaded into specific sessions
        without an explicit
        <command>LOAD</> command being given.  For
        example, <xref linkend="auto-explain"> could be enabled for all
        sessions under a given user name by setting this parameter
        with <command>ALTER ROLE SET</>.  Also, this parameter can be changed
        without restarting the server (but changes only take effect when a new
        session is started), so it is easier to add new modules this way, even
        if they should apply to all sessions.
       </para>

       <para>
        Unlike <xref linkend="guc-shared-preload-libraries">, there is no large
        performance advantage to loading a library at session start rather than
        when it is first used.  There is some advantage, however, when
        connection pooling is used.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-shared-preload-libraries" xreflabel="shared_preload_libraries">
      <term><varname>shared_preload_libraries</varname> (<type>string</type>)
      <indexterm>
       <primary><varname>shared_preload_libraries</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        This variable specifies one or more shared libraries to be preloaded at
        server start.  This parameter can only be set at server
        start.  If a specified library is not found, the server will fail to
        start.
       </para>

       <para>
        Some libraries need to perform certain operations that can only take
        place at postmaster start, such as allocating shared memory, reserving
        light-weight locks, or starting background workers.  Those libraries
        must be loaded at server start through this parameter.  See the
        documentation of each library for details.
       </para>

       <para>
        Other libraries can also be preloaded.  By preloading a shared library,
        the library startup time is avoided when the library is first used.
        However, the time to start each new server process might increase
        slightly, even if that process never uses the library.  So this
        parameter is recommended only for libraries that will be used in most
        sessions.  Also, changing this parameter requires a server restart, so
        this is not the right setting to use for short-term debugging tasks,
        say.  Use <xref linkend="guc-session-preload-libraries"> for that
        instead.
       </para>

      <note>
       <para>
        On Windows hosts, preloading a library at server start will not reduce
        the time required to start each new server process; each server process
        will re-load all preload libraries.  However, <varname>shared_preload_libraries
        </varname> is still useful on Windows hosts for libraries that need to
        perform operations at postmaster start time.
       </para>
      </note>
      </listitem>
     </varlistentry>
    </variablelist>
   </sect2>

     <sect2 id="runtime-config-client-other">
     <title>Other Defaults</title>

     <variablelist>

     <varlistentry id="guc-dynamic-library-path" xreflabel="dynamic_library_path">
      <term><varname>dynamic_library_path</varname> (<type>string</type>)
      <indexterm>
       <primary><varname>dynamic_library_path</> configuration parameter</primary>
      </indexterm>
      <indexterm><primary>dynamic loading</></>
      </term>
      <listitem>
       <para>
        If a dynamically loadable module needs to be opened and the
        file name specified in the <command>CREATE FUNCTION</command> or
        <command>LOAD</command> command
        does not have a directory component (i.e., the
        name does not contain a slash), the system will search this
        path for the required file.
       </para>

       <para>
        The value for <varname>dynamic_library_path</varname> must be a
        list of absolute directory paths separated by colons (or semi-colons
        on Windows).  If a list element starts
        with the special string <literal>$libdir</literal>, the
        compiled-in <productname>PostgreSQL</productname> package
        library directory is substituted for <literal>$libdir</literal>; this
        is where the modules provided by the standard
        <productname>PostgreSQL</productname> distribution are installed.
        (Use <literal>pg_config --pkglibdir</literal> to find out the name of
        this directory.) For example:
<programlisting>
dynamic_library_path = '/usr/local/lib/postgresql:/home/my_project/lib:$libdir'
</programlisting>
        or, in a Windows environment:
<programlisting>
dynamic_library_path = 'C:\tools\postgresql;H:\my_project\lib;$libdir'
</programlisting>
       </para>

       <para>
        The default value for this parameter is
        <literal>'$libdir'</literal>. If the value is set to an empty
        string, the automatic path search is turned off.
       </para>

       <para>
        This parameter can be changed at run time by superusers, but a
        setting done that way will only persist until the end of the
        client connection, so this method should be reserved for
        development purposes. The recommended way to set this parameter
        is in the <filename>postgresql.conf</filename> configuration
        file.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-gin-fuzzy-search-limit" xreflabel="gin_fuzzy_search_limit">
      <term><varname>gin_fuzzy_search_limit</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>gin_fuzzy_search_limit</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Soft upper limit of the size of the set returned by GIN index scans. For more
        information see <xref linkend="gin-tips">.
       </para>
      </listitem>
     </varlistentry>

     </variablelist>
    </sect2>
   </sect1>

   <sect1 id="runtime-config-locks">
    <title>Lock Management</title>

     <variablelist>

     <varlistentry id="guc-deadlock-timeout" xreflabel="deadlock_timeout">
      <term><varname>deadlock_timeout</varname> (<type>integer</type>)
      <indexterm>
       <primary>deadlock</primary>
       <secondary>timeout during</secondary>
      </indexterm>
      <indexterm>
       <primary>timeout</primary>
       <secondary>deadlock</secondary>
      </indexterm>
      <indexterm>
       <primary><varname>deadlock_timeout</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        This is the amount of time, in milliseconds, to wait on a lock
        before checking to see if there is a deadlock condition. The
        check for deadlock is relatively expensive, so the server doesn't run
        it every time it waits for a lock. We optimistically assume
        that deadlocks are not common in production applications and
        just wait on the lock for a while before checking for a
        deadlock. Increasing this value reduces the amount of time
        wasted in needless deadlock checks, but slows down reporting of
        real deadlock errors. The default is one second (<literal>1s</>),
        which is probably about the smallest value you would want in
        practice. On a heavily loaded server you might want to raise it.
        Ideally the setting should exceed your typical transaction time,
        so as to improve the odds that a lock will be released before
        the waiter decides to check for deadlock.  Only superusers can change
        this setting.
       </para>

       <para>
        When <xref linkend="guc-log-lock-waits"> is set,
        this parameter also determines the length of time to wait before
        a log message is issued about the lock wait.  If you are trying
        to investigate locking delays you might want to set a shorter than
        normal <varname>deadlock_timeout</varname>.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-max-locks-per-transaction" xreflabel="max_locks_per_transaction">
      <term><varname>max_locks_per_transaction</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>max_locks_per_transaction</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        The shared lock table tracks locks on
        <varname>max_locks_per_transaction</varname> * (<xref
        linkend="guc-max-connections"> + <xref
        linkend="guc-max-prepared-transactions">) objects (e.g.,  tables);
        hence, no more than this many distinct objects can be locked at
        any one time.  This parameter controls the average number of object
        locks allocated for each transaction;  individual transactions
        can lock more objects as long as the locks of all transactions
        fit in the lock table.  This is <emphasis>not</> the number of
        rows that can be locked; that value is unlimited.  The default,
        64, has historically proven sufficient, but you might need to
        raise this value if you have queries that touch many different
        tables in a single transaction, e.g. query of a parent table with
        many children.  This parameter can only be set at server start.
       </para>

       <para>
        When running a standby server, you must set this parameter to the
        same or higher value than on the master server. Otherwise, queries
        will not be allowed in the standby server.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-max-pred-locks-per-transaction" xreflabel="max_pred_locks_per_transaction">
      <term><varname>max_pred_locks_per_transaction</varname> (<type>integer</type>)
      <indexterm>
       <primary><varname>max_pred_locks_per_transaction</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        The shared predicate lock table tracks locks on
        <varname>max_pred_locks_per_transaction</varname> * (<xref
        linkend="guc-max-connections"> + <xref
        linkend="guc-max-prepared-transactions">) objects (e.g., tables);
        hence, no more than this many distinct objects can be locked at
        any one time.  This parameter controls the average number of object
        locks allocated for each transaction;  individual transactions
        can lock more objects as long as the locks of all transactions
        fit in the lock table.  This is <emphasis>not</> the number of
        rows that can be locked; that value is unlimited.  The default,
        64, has generally been sufficient in testing, but you might need to
        raise this value if you have clients that touch many different
        tables in a single serializable transaction. This parameter can
        only be set at server start.
       </para>

      </listitem>
     </varlistentry>

     </variablelist>
   </sect1>

   <sect1 id="runtime-config-compatible">
    <title>Version and Platform Compatibility</title>

    <sect2 id="runtime-config-compatible-version">
     <title>Previous PostgreSQL Versions</title>

     <variablelist>

     <varlistentry id="guc-array-nulls" xreflabel="array_nulls">
      <term><varname>array_nulls</varname> (<type>boolean</type>)
      <indexterm>
       <primary><varname>array_nulls</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        This controls whether the array input parser recognizes
        unquoted <literal>NULL</> as specifying a null array element.
        By default, this is <literal>on</>, allowing array values containing
        null values to be entered.  However, <productname>PostgreSQL</> versions
        before 8.2 did not support null values in arrays, and therefore would
        treat <literal>NULL</> as specifying a normal array element with
        the string value <quote>NULL</>.  For backward compatibility with
        applications that require the old behavior, this variable can be
        turned <literal>off</>.
       </para>

       <para>
        Note that it is possible to create array values containing null values
        even when this variable is <literal>off</>.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-backslash-quote" xreflabel="backslash_quote">
      <term><varname>backslash_quote</varname> (<type>enum</type>)
      <indexterm><primary>strings</><secondary>backslash quotes</></>
      <indexterm>
       <primary><varname>backslash_quote</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        This controls whether a quote mark can be represented by
        <literal>\'</> in a string literal.  The preferred, SQL-standard way
        to represent a quote mark is by doubling it (<literal>''</>) but
        <productname>PostgreSQL</> has historically also accepted
        <literal>\'</>. However, use of <literal>\'</> creates security risks
        because in some client character set encodings, there are multibyte
        characters in which the last byte is numerically equivalent to ASCII
        <literal>\</>.  If client-side code does escaping incorrectly then a
        SQL-injection attack is possible.  This risk can be prevented by
        making the server reject queries in which a quote mark appears to be
        escaped by a backslash.
        The allowed values of <varname>backslash_quote</> are
        <literal>on</> (allow <literal>\'</> always),
        <literal>off</> (reject always), and
        <literal>safe_encoding</> (allow only if client encoding does not
        allow ASCII <literal>\</> within a multibyte character).
        <literal>safe_encoding</> is the default setting.
       </para>

       <para>
        Note that in a standard-conforming string literal, <literal>\</> just
        means <literal>\</> anyway.  This parameter only affects the handling of
        non-standard-conforming literals, including
        escape string syntax (<literal>E'...'</>).
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-default-with-oids" xreflabel="default_with_oids">
      <term><varname>default_with_oids</varname> (<type>boolean</type>)
      <indexterm>
       <primary><varname>default_with_oids</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        This controls whether <command>CREATE TABLE</command> and
        <command>CREATE TABLE AS</command> include an OID column in
        newly-created tables, if neither <literal>WITH OIDS</literal>
        nor <literal>WITHOUT OIDS</literal> is specified. It also
        determines whether OIDs will be included in tables created by
        <command>SELECT INTO</command>. The parameter is <literal>off</>
        by default; in <productname>PostgreSQL</> 8.0 and earlier, it
        was <literal>on</> by default.
       </para>

       <para>
        The use of OIDs in user tables is considered deprecated, so
        most installations should leave this variable disabled.
        Applications that require OIDs for a particular table should
        specify <literal>WITH OIDS</literal> when creating the
        table. This variable can be enabled for compatibility with old
        applications that do not follow this behavior.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-escape-string-warning" xreflabel="escape_string_warning">
      <term><varname>escape_string_warning</varname> (<type>boolean</type>)
      <indexterm><primary>strings</><secondary>escape warning</></>
      <indexterm>
       <primary><varname>escape_string_warning</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        When on, a warning is issued if a backslash (<literal>\</>)
        appears in an ordinary string literal (<literal>'...'</>
        syntax) and <varname>standard_conforming_strings</varname> is off.
        The default is <literal>on</>.
       </para>
       <para>
        Applications that wish to use backslash as escape should be
        modified to use escape string syntax (<literal>E'...'</>),
        because the default behavior of ordinary strings is now to treat
        backslash as an ordinary character, per SQL standard.  This variable
        can be enabled to help locate code that needs to be changed.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-lo-compat-privileges" xreflabel="lo_compat_privileges">
      <term><varname>lo_compat_privileges</varname> (<type>boolean</type>)
      <indexterm>
       <primary><varname>lo_compat_privileges</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        In <productname>PostgreSQL</> releases prior to 9.0, large objects
        did not have access privileges and were, therefore, always readable
        and writable by all users.  Setting this variable to <literal>on</>
        disables the new privilege checks, for compatibility with prior
        releases.  The default is <literal>off</>.
        Only superusers can change this setting.
       </para>
       <para>
        Setting this variable does not disable all security checks related to
        large objects &mdash; only those for which the default behavior has
        changed in <productname>PostgreSQL</> 9.0.
        For example, <literal>lo_import()</literal> and
        <literal>lo_export()</literal> need superuser privileges regardless
        of this setting.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-operator-precedence-warning" xreflabel="operator_precedence_warning">
      <term><varname>operator_precedence_warning</varname> (<type>boolean</type>)
      <indexterm>
       <primary><varname>operator_precedence_warning</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        When on, the parser will emit a warning for any construct that might
        have changed meanings since <productname>PostgreSQL</> 9.4 as a result
        of changes in operator precedence.  This is useful for auditing
        applications to see if precedence changes have broken anything; but it
        is not meant to be kept turned on in production, since it will warn
        about some perfectly valid, standard-compliant SQL code.
        The default is <literal>off</>.
       </para>

       <para>
        See <xref linkend="sql-precedence"> for more information.
       </para>
      </listitem>
     </varlistentry>

    <varlistentry id="guc-quote-all-identifiers" xreflabel="quote-all-identifiers">
      <term><varname>quote_all_identifiers</varname> (<type>boolean</type>)
      <indexterm>
       <primary><varname>quote_all_identifiers</> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        When the database generates SQL, force all identifiers to be quoted,
        even if they are not (currently) keywords.  This will affect the
        output of <command>EXPLAIN</> as well as the results of functions
        like <function>pg_get_viewdef</>.  See also the
        <option>--quote-all-identifiers</option> option of
        <xref linkend="app-pgdump"> and <xref linkend="app-pg-dumpall">.