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
|
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<title>DB->compact()</title>
<link rel="stylesheet" href="apiReference.css" type="text/css" />
<meta name="generator" content="DocBook XSL Stylesheets V1.73.2" />
<link rel="start" href="index.html" title="Berkeley DB C API Reference" />
<link rel="up" href="db.html" title="Chapter 2. The DB Handle" />
<link rel="prev" href="dbcreate.html" title="db_create" />
<link rel="next" href="dbdel.html" title="DB->del()" />
</head>
<body>
<div class="navheader">
<table width="100%" summary="Navigation header">
<tr>
<th colspan="3" align="center">DB->compact()</th>
</tr>
<tr>
<td width="20%" align="left"><a accesskey="p" href="dbcreate.html">Prev</a> </td>
<th width="60%" align="center">Chapter 2.
The DB Handle
</th>
<td width="20%" align="right"> <a accesskey="n" href="dbdel.html">Next</a></td>
</tr>
</table>
<hr />
</div>
<div class="sect1" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h2 class="title" style="clear: both"><a id="dbcompact"></a>DB->compact()</h2>
</div>
</div>
</div>
<pre class="programlisting">#include <db.h>
int
DB->compact(DB *db, DB_TXN *txnid,
DBT *start, DBT *stop, DB_COMPACT *c_data, u_int32_t flags, DBT *end); </pre>
<p>
The <code class="methodname">DB->compact()</code> method compacts Btree and Recno access method
databases, and optionally returns unused Btree, Hash or Recno database
pages to the underlying filesystem.
</p>
<p>
The <code class="methodname">DB->compact()</code> <span>
<span>
method returns a non-zero error value on failure and 0 on success.
</span>
</span>
</p>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="id1632862"></a>Parameters</h3>
</div>
</div>
</div>
<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="id1632429"></a>txnid</h4>
</div>
</div>
</div>
<p>
If the operation is part of an application-specified transaction, the
<span class="bold"><strong>txnid</strong></span> parameter is a transaction
handle returned from <a class="xref" href="txnbegin.html" title="DB_ENV->txn_begin()">DB_ENV->txn_begin()</a>;
if the operation is part of a Berkeley DB Concurrent Data Store group, the
<span class="bold"><strong>txnid</strong></span> parameter is a handle returned
from <a class="xref" href="envcdsgroup_begin.html" title="DB_ENV->cdsgroup_begin()">DB_ENV->cdsgroup_begin()</a>;
otherwise NULL.
</p>
<p>
If a transaction handle is supplied to this method, then the operation is
performed using that transaction. In this event, large sections of the
tree may be locked during the course of the transaction.
</p>
<p>
If no transaction handle is specified, but the operation occurs
in a transactional database, the operation will be implicitly
transaction protected using multiple transactions. These transactions
will be periodically committed to avoid locking large sections of the
tree. Any deadlocks encountered cause the compaction operation to
be retried from the point of the last transaction commit.
</p>
</div>
<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="id1632702"></a>start</h4>
</div>
</div>
</div>
<p>
If non-NULL, the <span class="bold"><strong>start</strong></span> parameter is
the starting point for compaction in a Btree or Recno database.
Compaction will start at the smallest key greater than or equal to the
specified key. If NULL, compaction will start at the beginning of the
database.
</p>
</div>
<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="id1632903"></a>stop</h4>
</div>
</div>
</div>
<p>
If non-NULL, the <span class="bold"><strong>stop</strong></span> parameter is
the stopping point for compaction in a Btree or Recno database.
Compaction will stop at the page with the smallest key greater than
the specified key. If NULL, compaction will stop at the end of the
database.
</p>
</div>
<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="id1632651"></a>c_data</h4>
</div>
</div>
</div>
<p>
</p>
<p>
If non-NULL, the <span class="bold"><strong>c_data</strong></span> parameter
contains additional compaction configuration parameters, and returns
compaction operation statistics, in a structure of type DB_COMPACT.
</p>
<p>
The following input configuration fields are available from the
DB_COMPACT structure:
</p>
<div class="itemizedlist">
<ul type="disc">
<li>
<p>
<code class="literal">int compact_fillpercent;</code>
</p>
<p>
If non-zero, this provides the goal for filling pages, specified as a percentage
between 1 and 100. Any page in a Btree or Recno databases not at or
above this percentage full will be considered for compaction. The
default behavior is to consider every page for compaction, regardless
of its page fill percentage.
</p>
</li>
<li>
<p>
<code class="literal">int compact_pages;</code>
</p>
<p>
If non-zero, the call will return after the
specified number of pages have been freed, or
no more pages can be freed.
</p>
</li>
<li>
<p>
<code class="literal">db_timeout_t compact_timeout;</code>
</p>
<p>
If non-zero, and no <span class="bold"><strong>txnid</strong></span> parameter
was specified, this parameter identifies the lock timeout used for implicit transactions, in
microseconds.
</p>
</li>
</ul>
</div>
<p>
The following output statistics fields are available from the
<code class="literal">DB_COMPACT</code> structure:
</p>
<div class="itemizedlist">
<ul type="disc">
<li>
<p>
<code class="literal">u_int32_t compact_deadlock;</code>
</p>
<p>
An output statistics parameter: if no <span class="bold"><strong>txnid</strong></span> parameter was specified, the number of
deadlocks which occurred.
</p>
</li>
<li>
<p>
<code class="literal">u_int32_t compact_pages_examine;</code>
</p>
<p>
An output statistics parameter: the number of database pages reviewed
during the compaction phase.
</p>
</li>
<li>
<p>
<code class="literal">u_int32_t compact_pages_free;</code>
</p>
<p>
An output statistics parameter: the number of database pages freed
during the compaction phase.
</p>
</li>
<li>
<p>
<code class="literal">u_int32_t compact_levels;</code>
</p>
<p>
An output statistics parameter: the number of levels removed from the
Btree or Recno database during the compaction phase.
</p>
</li>
<li>
<p>
<code class="literal">u_int32_t compact_pages_truncated;</code>
</p>
<p>
An output statistics parameter: the number of database pages returned
to the filesystem.
</p>
</li>
</ul>
</div>
</div>
<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="id1632483"></a>flags</h4>
</div>
</div>
</div>
<p>
The <span class="bold"><strong>flags</strong></span> parameter must be set to 0
or one of the following values:
</p>
<div class="itemizedlist">
<ul type="disc">
<li>
<p><a id="compact_DB_FREELIST_ONLY"></a>
<code class="literal">DB_FREELIST_ONLY</code>
</p>
<p>
Do no page compaction, only returning pages to the filesystem that are
already free and at the end of the file. This flag must be set if the
database is a Hash access method database.
</p>
</li>
<li>
<p><a id="compact_DB_FREE_SPACE"></a>
<code class="literal">DB_FREE_SPACE</code>
</p>
<p>
Return pages to the filesystem when possible. If this flag is not
specified, pages emptied as a result of compaction will be placed on
the free list for re-use, but never returned to the filesystem.
</p>
<p>
Note that only pages at the end of a file can be returned to the
filesystem. Because of the one-pass nature of the compaction
algorithm, any unemptied page near the end of the file inhibits
returning pages to the file system. A repeated call to the
<code class="methodname">DB->compact()</code> method with a low <span class="bold"><strong>compact_fillpercent</strong></span> may be used to return pages
in this case.
</p>
</li>
</ul>
</div>
</div>
<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="id1633063"></a>end</h4>
</div>
</div>
</div>
<p>
If non-NULL, the <span class="bold"><strong>end</strong></span> parameter will
be filled in with the database key marking the end of the compaction
operation in a Btree or Recno database. This is generally the first
key of the page where the operation stopped.
</p>
</div>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="id1633231"></a>Errors</h3>
</div>
</div>
</div>
<p>
The <code class="methodname">DB->compact()</code> <span>
<span>
method may fail and return one of the following non-zero errors:
</span>
</span>
</p>
<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="id1632714"></a>DB_LOCK_DEADLOCK</h4>
</div>
</div>
</div>
<p>
A transactional database environment operation was selected to resolve
a deadlock.
</p>
</div>
<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="id1633322"></a>DB_LOCK_NOTGRANTED</h4>
</div>
</div>
</div>
<p>
A Berkeley DB Concurrent Data Store database environment configured
for lock timeouts was unable to grant a lock in the allowed time.
</p>
</div>
<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="id1633040"></a> DB_REP_HANDLE_DEAD</h4>
</div>
</div>
</div>
<p>
When a client synchronizes with the master, it is possible for committed
transactions to be rolled back. This invalidates all the database and cursor
handles opened in the replication environment. Once this occurs, an attempt to use
such a handle will
return <code class="literal">DB_REP_HANDLE_DEAD</code>.
The application will need to discard the handle and open a new one in order to
continue processing.
</p>
</div>
<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="id1633331"></a>DB_REP_LOCKOUT</h4>
</div>
</div>
</div>
<p>
The operation was blocked by client/master synchronization.
</p>
</div>
<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="id1632885"></a>EACCES</h4>
</div>
</div>
</div>
<p>
An attempt was made to modify a read-only database.
</p>
</div>
<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="id1633333"></a>EINVAL</h4>
</div>
</div>
</div>
<p>
An invalid flag value or parameter was specified.
</p>
</div>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="id1633048"></a>Class</h3>
</div>
</div>
</div>
<p>
<a class="link" href="db.html" title="Chapter 2. The DB Handle">DB</a>
</p>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="id1632779"></a>See Also</h3>
</div>
</div>
</div>
<p>
<a class="xref" href="db.html#dblist" title="Database and Related Methods">Database and Related Methods</a>
</p>
</div>
</div>
<div class="navfooter">
<hr />
<table width="100%" summary="Navigation footer">
<tr>
<td width="40%" align="left"><a accesskey="p" href="dbcreate.html">Prev</a> </td>
<td width="20%" align="center">
<a accesskey="u" href="db.html">Up</a>
</td>
<td width="40%" align="right"> <a accesskey="n" href="dbdel.html">Next</a></td>
</tr>
<tr>
<td width="40%" align="left" valign="top">db_create </td>
<td width="20%" align="center">
<a accesskey="h" href="index.html">Home</a>
</td>
<td width="40%" align="right" valign="top"> DB->del()</td>
</tr>
</table>
</div>
</body>
</html>
|
