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
|
set @@global.optimizer_switch=@@local.optimizer_switch;
set @@global.join_cache_level=@@local.join_cache_level;
DROP TABLE IF EXISTS t1;
CREATE TABLE t1
(a INT AUTO_INCREMENT PRIMARY KEY,
b CHAR(20)
);
SET @start_value= @@global.max_seeks_for_key;
'#--------------------FN_DYNVARS_084_01-------------------------#'
CONNECT test_con1,localhost,root,,;
connection test_con1;
SET @@global.max_seeks_for_key = 20;
SELECT @@global.max_seeks_for_key;
@@global.max_seeks_for_key
20
INSERT INTO t1(b) VALUES("AREc");
EXPLAIN SELECT STRAIGHT_JOIN * FROM t1,t1 AS t2 WHERE t1.b = t2.b;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 system NULL NULL NULL NULL 1
1 SIMPLE t2 system NULL NULL NULL NULL 1
SET @@session.max_seeks_for_key = 2;
SELECT @@session.max_seeks_for_key;
@@session.max_seeks_for_key
2
INSERT INTO t1(b) VALUES("BREc");
INSERT INTO t1(b) VALUES("CRec");
EXPLAIN SELECT STRAIGHT_JOIN * FROM t1,t1 AS t2 WHERE t1.b = t2.b;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ALL NULL NULL NULL NULL 3
1 SIMPLE t2 ALL NULL NULL NULL NULL 3 Using where; Using join buffer (flat, BNL join)
'#--------------------FN_DYNVARS_084_02-------------------------#'
CONNECT test_con2,localhost,root,,;
connection test_con2;
SELECT @@global.max_seeks_for_key = 10;
@@global.max_seeks_for_key = 10
0
SELECT @@session.max_seeks_for_key = 10;
@@session.max_seeks_for_key = 10
0
SET @@global.max_seeks_for_key = 20;
SELECT @@global.max_seeks_for_key;
@@global.max_seeks_for_key
20
INSERT INTO t1(b) VALUES("AREc");
EXPLAIN SELECT STRAIGHT_JOIN * FROM t1,t1 AS t2 WHERE t1.b = t2.b;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ALL NULL NULL NULL NULL 4
1 SIMPLE t2 ALL NULL NULL NULL NULL 4 Using where; Using join buffer (flat, BNL join)
SET @@session.max_seeks_for_key = 2;
SELECT @@session.max_seeks_for_key;
@@session.max_seeks_for_key
2
INSERT INTO t1(b) VALUES("BREc");
INSERT INTO t1(b) VALUES("CRec");
EXPLAIN SELECT STRAIGHT_JOIN * FROM t1,t1 AS t2 WHERE t1.b = t2.b;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ALL NULL NULL NULL NULL 6
1 SIMPLE t2 ALL NULL NULL NULL NULL 6 Using where; Using join buffer (flat, BNL join)
INSERT INTO t1 VALUES(null,"test");
INSERT INTO t1 VALUES (null,"a"),(null,"a"),(null,"a"),
(null,"a"),(null,"a"),(null,"a"),(null,"a"),
(null,"a"),(null,"a"),(null,"a");
EXPLAIN SELECT STRAIGHT_JOIN * FROM t1,t1 AS t2 WHERE t1.b = t2.b;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ALL NULL NULL NULL NULL 17
1 SIMPLE t2 ALL NULL NULL NULL NULL 17 Using where; Using join buffer (flat, BNL join)
ANALYZE TABLE t1;
Table Op Msg_type Msg_text
test.t1 analyze status Engine-independent statistics collected
test.t1 analyze status OK
SET MAX_SEEKS_FOR_KEY=1;
EXPLAIN SELECT STRAIGHT_JOIN * FROM t1,t1 AS t2 WHERE t1.b = t2.b;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ALL NULL NULL NULL NULL 17
1 SIMPLE t2 ALL NULL NULL NULL NULL 17 Using where; Using join buffer (flat, BNL join)
SET MAX_SEEKS_FOR_KEY=DEFAULT;
connection default;
disconnect test_con1;
disconnect test_con2;
DROP TABLE t1;
SET @@global.max_seeks_for_key= @start_value;
SET @@global.optimizer_switch= @save_optimizer_switch;
SET @@global.join_cache_level= @save_join_cache_level;
|
