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作者：惜分飞©版权所有[未经本人同意,不得以任何形式转载,否则有进一步追究法律责任的权利.]
一个复杂的sql查询,使用了大量EXISTS和NOT EXISTS 关联导致sql执行效率低下,这里挑选出来最核心的部分进行演示
SQL> explain plan for select
2 a.aab034, a.aac001
3 from si_dp.ac01_ac02 a
4 where exists (select 1
5 from ic40
6 where aac001 = a.aac001
7 and aae045 <= '201803'
8 and aae120 = '0')
9 and not exists (select 1
10 from ic15
11 where aac001 = a.aac001
12 and aae002 <= '201803')
13 and not EXISTS (select aab001
14 from ab01
15 where aab019 in ('91', '93')
16 AND aab001 = a.aab001)
17 and exists (select 1
18 from ac13
19 where aac001 = a.aac001
20 and aae140 = '11'
21 and aae114 in ('0', '1')
22 and aae002 <= '201803')
23 AND EXISTS (SELECT 1
24 FROM AC13
25 WHERE AAC001 = A.AAC001
26 and aae140 = '11'
27 AND AAE143 = '02'
28 AND AAE003 < '201707'
29 AND AAE002 BETWEEN '201801' AND '201803'
30 and aae114 = '1')
31 AND not EXISTS (SELECT 1
32 FROM AC13
33 WHERE AAC001 = A.AAC001
34 and aae140 = '11'
35 AND AAE002 < '201801')
36 AND not EXISTS (SELECT 1
37 FROM ac02
38 WHERE AAC001 = A.AAC001
39 and aae140 = '11'
40 AND AAE036 < date '2018-1-1');
Explained.
Elapsed: 00:00:00.36
SQL> select * from table (dbms_xplan.display);
PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------------------------------
-----------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes |TempSpc| Cost (%CPU)|
-----------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 202 | | 11172 (2)|
| 1 | NESTED LOOPS SEMI | | 1 | 202 | | 11172 (2)|
| 2 | NESTED LOOPS ANTI | | 1 | 175 | | 11168 (2)|
| 3 | NESTED LOOPS SEMI | | 1 | 150 | | 11164 (2)|
| 4 | NESTED LOOPS ANTI | | 1 | 126 | | 11160 (2)|
| 5 | NESTED LOOPS SEMI | | 1 | 104 | | 11158 (2)|
| 6 | NESTED LOOPS ANTI | | 1 | 67 | | 11145 (2)|
| 7 | HASH JOIN ANTI | | 1 | 50 | 8640K| 11143 (2)|
| 8 | TABLE ACCESS FULL | AC01_AC02 | 245K| 5755K| | 356 (2)|
| 9 | TABLE ACCESS FULL | AC02 | 559K| 13M| | 9346 (2)|
| 10 | TABLE ACCESS BY INDEX ROWID| AB01 | 2 | 34 | | 2 (0)|
| 11 | INDEX UNIQUE SCAN | PK_AB01 | 1 | | | 1 (0)|
| 12 | TABLE ACCESS BY INDEX ROWID | AC13 | 325K| 11M| | 13 (0)|
| 13 | INDEX RANGE SCAN | I_AC13_AAE143 | 446 | | | 4 (0)|
| 14 | INDEX RANGE SCAN | PK_IC15 | 1771K| 37M| | 2 (0)|
| 15 | TABLE ACCESS BY INDEX ROWID | IC40 | 17M| 395M| | 4 (0)|
| 16 | INDEX RANGE SCAN | PK_IC40 | 1 | | | 3 (0)|
| 17 | TABLE ACCESS BY INDEX ROWID | AC13 | 51M| 1236M| | 4 (0)|
| 18 | INDEX RANGE SCAN | RELATION_233112_FK | 3 | | | 3 (0)|
| 19 | TABLE ACCESS BY INDEX ROWID | AC13 | 52M| 1350M| | 4 (0)|
| 20 | INDEX RANGE SCAN | RELATION_233112_FK | 3 | | | 3 (0)|
-----------------------------------------------------------------------------------------------------
这条sql,在一个10.2.0.3的系统中执行了十几个小时无法出结果,开发商反馈,该大部分客户的11.2的环境中,大概十几分钟出结果.从来没有遇到此类情况.让我们给他优化sql.看到这个sql,第一反应就是很可能大量的NESTED LOOPS效率低下,怀疑统计信息错误,结果收集完统计信息之后,执行计划依旧,我就在思考怎么调整sql,让其不这样大量嵌套执行.想起来的_unnest_subquery是控制子查询嵌套转换的,从9i开始默认为true,尝试设置为false测试.
SQL> alter session set "_unnest_subquery"=false;
Session altered.
Elapsed: 00:00:00.00
SQL> explain plan for select
2 a.aab034, a.aac001
3 from si_dp.ac01_ac02 a
4 where exists (select 1
5 from ic40
6 where aac001 = a.aac001
7 and aae045 <= '201803'
8 and aae120 = '0')
9 and not exists (select 1
10 from ic15
11 where aac001 = a.aac001
12 and aae002 <= '201803')
13 and not EXISTS (select aab001
14 from ab01
15 where aab019 in ('91', '93')
16 AND aab001 = a.aab001)
17 and exists (select 1
18 from ac13
19 where aac001 = a.aac001
20 and aae140 = '11'
21 and aae114 in ('0', '1')
22 and aae002 <= '201803')
23 AND EXISTS (SELECT 1
24 FROM AC13
25 WHERE AAC001 = A.AAC001
26 and aae140 = '11'
27 AND AAE143 = '02'
28 AND AAE003 < '201707'
29 AND AAE002 BETWEEN '201801' AND '201803'
30 and aae114 = '1')
31 AND not EXISTS (SELECT 1
32 FROM AC13
33 WHERE AAC001 = A.AAC001
34 and aae140 = '11'
35 AND AAE002 < '201801')
36 AND not EXISTS (SELECT 1
37 FROM ac02
38 WHERE AAC001 = A.AAC001
39 and aae140 = '11'
40 AND AAE036 < date '2018-1-1');
Explained.
Elapsed: 00:00:00.07
SQL> select * from table (dbms_xplan.display);
PLAN_TABLE_OUTPUT
-----------------------------------------------------------------------------------------------
-----------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes |TempSpc| Cost (%CPU)|
-----------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 185K| 19M| | 2991K (2)|
| 1 | FILTER | | | | | |
| 2 | HASH JOIN RIGHT SEMI | | 185K| 19M| 16M| 758K (3)|
| 3 | TABLE ACCESS BY INDEX ROWID| AC13 | 353K| 12M| | 4556 (1)|
| 4 | INDEX SKIP SCAN | I_AC13_AAB001 | 23608 | | | 2287 (1)|
| 5 | HASH JOIN SEMI | | 201K| 14M| 11M| 751K (3)|
| 6 | HASH JOIN SEMI | | 201K| 9452K| 8640K| 123K (3)|
| 7 | TABLE ACCESS FULL | AC01_AC02 | 245K| 5755K| | 357 (2)|
| 8 | TABLE ACCESS FULL | IC40 | 21M| 481M| | 86122 (3)|
| 9 | TABLE ACCESS FULL | AC13 | 52M| 1350M| | 530K (3)|
| 10 | INDEX RANGE SCAN | PK_IC15 | 2 | 44 | | 3 (0)|
| 11 | VIEW | index$_join$_009 | 1 | 17 | | 3 (34)|
| 12 | HASH JOIN | | | | | |
| 13 | INDEX RANGE SCAN | PK_AB01 | 1 | 17 | | 2 (0)|
| 14 | INLIST ITERATOR | | | | | |
| 15 | INDEX RANGE SCAN | IDX_AB01_AAB019 | 1 | 17 | | 8 (0)|
| 16 | TABLE ACCESS BY INDEX ROWID | AC13 | 2 | 50 | | 5 (0)|
| 17 | INDEX RANGE SCAN | I_AC13_SEARCH | 152 | | | 4 (0)|
| 18 | TABLE ACCESS BY INDEX ROWID | AC02 | 1 | 26 | | 4 (0)|
| 19 | INDEX RANGE SCAN | PK_AC02 | 1 | | | 3 (0)|
-----------------------------------------------------------------------------------------------
让开发设置该参数,然后执行sql,结果3分钟不到出结果,非常圆满完成任务.该sql还有进一步优化空间,但是考虑到已经满足要求,不再折腾.