Oracle之SQL优化专题02-稳固SQL执行计划的方法
2018-11-05 03:32 AlfredZhao 阅读(886) 评论(0) 编辑 收藏 举报首先构建一个简单的测试用例来实际演示：
create table emp as select * from scott.emp;
create table dept as select * from scott.dept;
create index idx_emp_empno on emp(empno);
create index idx_dept_deptno on dept(deptno);
测试过程中查看真实执行计划的方法：
set lines 1000 pages 1000
alter session set statistics_level = ALL;
Execute SQL;
select * from table(dbms_xplan.display_cursor(null,null,'allstats last'));
正常的SQL执行，执行计划会走相应的索引：
--good SQL: 39dv3d8jkzyuw
select a.empno, a.ename, b.dname, a.job, a.sal from emp a, dept b where a.deptno = b.deptno and empno = 7788;
--good xplan: 1725450077
SQL> select * from table(dbms_xplan.display_cursor(null,null,'allstats last'));
PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
SQL_ID 39dv3d8jkzyuw, child number 0
-------------------------------------
select a.empno, a.ename, b.dname, a.job, a.sal from emp a, dept b where
a.deptno = b.deptno and empno = 7788
Plan hash value: 1725450077
--------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers | Reads |
--------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | 1 |00:00:00.01 | 6 | 2 |
| 1 | NESTED LOOPS | | 1 | 1 | 1 |00:00:00.01 | 6 | 2 |
| 2 | NESTED LOOPS | | 1 | 1 | 1 |00:00:00.01 | 5 | 2 |
| 3 | TABLE ACCESS BY INDEX ROWID| EMP | 1 | 1 | 1 |00:00:00.01 | 3 | 1 |
|* 4 | INDEX RANGE SCAN | IDX_EMP_EMPNO | 1 | 1 | 1 |00:00:00.01 | 2 | 1 |
|* 5 | INDEX RANGE SCAN | IDX_DEPT_DEPTNO | 1 | 1 | 1 |00:00:00.01 | 2 | 1 |
| 6 | TABLE ACCESS BY INDEX ROWID | DEPT | 1 | 1 | 1 |00:00:00.01 | 1 | 0 |
--------------------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
4 - access("EMPNO"=7788)
5 - access("A"."DEPTNO"="B"."DEPTNO")
糟糕的SQL执行，执行计划走全表扫描（这里实验直接利用使用hint强制不走索引来模拟这种情况）:
--bad SQL: dqd10y7wqrg7f
select /*+ no_index(a idx_emp_empno) no_index(b idx_dept_deptno)*/a.empno, a.ename, b.dname, a.job, a.sal from emp a, dept b where a.deptno = b.deptno and empno = 7788;
--bad xplan: 1123238657
SQL> select * from table(dbms_xplan.display_cursor(null,null,'allstats last'));
PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
SQL_ID dqd10y7wqrg7f, child number 1
-------------------------------------
select /*+ no_index(a idx_emp_empno) no_index(b
idx_dept_deptno)*/a.empno, a.ename, b.dname, a.job, a.sal from emp a,
dept b where a.deptno = b.deptno and empno = 7788
Plan hash value: 1123238657
----------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers | OMem | 1Mem | Used-Mem |
----------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | 1 |00:00:00.01 | 5 | | | |
|* 1 | HASH JOIN | | 1 | 1 | 1 |00:00:00.01 | 5 | 1214K| 1214K| 377K (0)|
|* 2 | TABLE ACCESS FULL| EMP | 1 | 1 | 1 |00:00:00.01 | 2 | | | |
| 3 | TABLE ACCESS FULL| DEPT | 1 | 4 | 4 |00:00:00.01 | 3 | | | |
----------------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - access("A"."DEPTNO"="B"."DEPTNO")
2 - filter("EMPNO"=7788)
假设此时这些糟糕的SQL就是业务实际的SQL，且对应开发人员无法更改SQL文本（这里就是指无法去掉不走索引的hint），那么现在如何能将这些糟糕的SQL绑定成走索引的执行计划呢？
糟糕的SQL清单：
select /*+ no_index(a idx_emp_empno) no_index(b idx_dept_deptno)*/a.empno, a.ename, b.dname, a.job, a.sal from emp a, dept b where a.deptno = b.deptno and empno = 7788;
select /*+ no_index(a idx_emp_empno) no_index(b idx_dept_deptno)*/a.empno, a.ename, b.dname, a.job, a.sal from emp a, dept b where a.deptno = b.deptno and empno = 7900;
如何让其走索引？目前Oracle常见的2种稳固执行计划的方式：
1.SQL Profile稳固执行计划
适用于Oracle 10g及以上版本。 利用MOS文档215187.1提供的系列脚本中的coe_xfr_sql_profile.sql来稳固执行计划，只需要输入要调整SQL的SQL_ID和好的执行计划的plan_hash_value即可，脚本内容可参考：在本次演示实验中，就是将sql_id='dqd10y7wqrg7f'的SQL绑定好的plan_hash_value=1725450077，具体使用过程如下：
SQL> @coe_xfr_sql_profile.sql
Parameter 1:
SQL_ID (required)
Enter value for 1: dqd10y7wqrg7f
PLAN_HASH_VALUE AVG_ET_SECS
--------------- -----------
1123238657 .095
Parameter 2:
PLAN_HASH_VALUE (required)
Enter value for 2: 1725450077
Values passed to coe_xfr_sql_profile:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
SQL_ID : "dqd10y7wqrg7f"
PLAN_HASH_VALUE: "1725450077"
...
Execute coe_xfr_sql_profile_dqd10y7wqrg7f_1725450077.sql
on TARGET system in order to create a custom SQL Profile
with plan 1725450077 linked to adjusted sql_text.
COE_XFR_SQL_PROFILE completed.
然后按照提示执行生成的coe_xfr_sql_profile_dqd10y7wqrg7f_1725450077.sql脚本即可；
需要特别注意的是：可以根据实际情况是否需要修改这个脚本中的force_match的值为true。
本次的例子，就是没有使用到绑定变量，而需求是不仅让empno = 7788的条件走索引，还要让其他输入值，比如empno = 7900也同样走索引，那就需要修改这个force_match的值为true。稳固执行计划的效果如下：
SQL> select /*+ no_index(a idx_emp_empno) no_index(b idx_dept_deptno)*/a.empno, a.ename, b.dname, a.job, a.sal from emp a, dept b where a.deptno = b.deptno and empno = 7788;
EMPNO ENAME DNAME JOB SAL
---------- ---------- -------------- --------- ----------
7788 SCOTT RESEARCH ANALYST 3000
SQL> select * from table(dbms_xplan.display_cursor(null,null,'allstats last'));
PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
SQL_ID dqd10y7wqrg7f, child number 0
-------------------------------------
select /*+ no_index(a idx_emp_empno) no_index(b
idx_dept_deptno)*/a.empno, a.ename, b.dname, a.job, a.sal from emp a,
dept b where a.deptno = b.deptno and empno = 7788
Plan hash value: 1725450077
-----------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers |
-----------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | 1 |00:00:00.01 | 6 |
| 1 | NESTED LOOPS | | 1 | 1 | 1 |00:00:00.01 | 6 |
| 2 | NESTED LOOPS | | 1 | 1 | 1 |00:00:00.01 | 5 |
| 3 | TABLE ACCESS BY INDEX ROWID| EMP | 1 | 1 | 1 |00:00:00.01 | 3 |
|* 4 | INDEX RANGE SCAN | IDX_EMP_EMPNO | 1 | 1 | 1 |00:00:00.01 | 2 |
|* 5 | INDEX RANGE SCAN | IDX_DEPT_DEPTNO | 1 | 1 | 1 |00:00:00.01 | 2 |
| 6 | TABLE ACCESS BY INDEX ROWID | DEPT | 1 | 1 | 1 |00:00:00.01 | 1 |
-----------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
4 - access("EMPNO"=7788)
5 - access("A"."DEPTNO"="B"."DEPTNO")
Note
-----
- SQL profile coe_dqd10y7wqrg7f_1725450077 used for this statement
常用操作：
1)查询sql_profile
可以通过查询dba_sql_profiles来确认数据库中的sql_profile：
select * from dba_sql_profiles;
2)删除sql_profile
如果有一天不再需要这个sql_profile来稳固执行计划，可以这样删除sql_profile：
exec dbms_sqltune.drop_sql_profile('name');
exec dbms_sqltune.drop_sql_profile('coe_dqd10y7wqrg7f_1725450077');
3)清除SQL执行计划
还可以清除共享池中指定SQL的执行计划：
exec sys.dbms_shared_pool.purge('address,hash_value','c');
SQL> select sql_id, address, hash_value, plan_hash_value, sql_profile from v$sql where sql_id = 'dqd10y7wqrg7f';
SQL_ID ADDRESS HASH_VALUE PLAN_HASH_VALUE SQL_PROFILE
------------- ---------------- ---------- --------------- ----------------------------------------------------------------
dqd10y7wqrg7f 0000000076B909F8 4184587502 1123238657
dqd10y7wqrg7f 0000000076B909F8 4184587502 1123238657
dqd10y7wqrg7f 0000000076B909F8 4184587502 1725450077 coe_dqd10y7wqrg7f_1725450077
SQL> exec sys.dbms_shared_pool.purge('0000000076B909F8,4184587502','c');
PL/SQL procedure successfully completed.
SQL> select sql_id, address, hash_value, plan_hash_value, sql_profile from v$sql where sql_id = 'dqd10y7wqrg7f';
no rows selected
2.SPM稳固执行计划
适用于Oracle 11g及以上版本。 删除掉之前的sql_profile，尝试使用SPM来稳固执行计划，实际上，手工生成sql_plan_baseline的方式要更加灵活，但我实际用的比较少。 查看sql_plan_baselines：select * from dba_sql_plan_baselines;
select sql_handle, plan_name, origin, enabled, accepted, fixed from dba_sql_plan_baselines;
SPM稳固执行计划方法：
var temp number
--1.bad: sql_id & plan_hash_value
exec :temp := dbms_spm.load_plans_from_cursor_cache(sql_id => '', plan_hash_value => );
--2.good: sql_id & plan_hash_value & sql_handle
exec :temp := dbms_spm.load_plans_from_cursor_cache(sql_id => '', plan_hash_value => , sql_handle => );
--3.drop bad plan_name
exec :temp := dbms_spm.drop_sql_plan_baseline(sql_handle => '', plan_name => '');
用上面的例子具体说明：
--1.bad: sql_id & plan_hash_value
SQL> var temp number
SQL> exec :temp := dbms_spm.load_plans_from_cursor_cache(sql_id => 'dqd10y7wqrg7f', plan_hash_value => 1123238657);
SQL> select sql_handle, plan_name, origin, enabled, accepted, fixed from dba_sql_plan_baselines;
SQL_HANDLE PLAN_NAME ORIGIN ENA ACC FIX
------------------------------ ------------------------------ -------------- --- --- ---
SQL_9c3626a309e5e8bd SQL_PLAN_9sdj6nc4ybu5x96fd8705 MANUAL-LOAD YES YES NO
--2.good: sql_id & plan_hash_value & sql_handle（上面查到的）
SQL> exec :temp := dbms_spm.load_plans_from_cursor_cache(sql_id => '39dv3d8jkzyuw', plan_hash_value =>1725450077, sql_handle => 'SQL_9c3626a309e5e8bd');
PL/SQL procedure successfully completed.
SQL> select sql_handle, plan_name, origin, enabled, accepted, fixed from dba_sql_plan_baselines;
SQL_HANDLE PLAN_NAME ORIGIN ENA ACC FIX
------------------------------ ------------------------------ -------------- --- --- ---
SQL_9c3626a309e5e8bd SQL_PLAN_9sdj6nc4ybu5x2b78d17a MANUAL-LOAD YES YES NO
SQL_9c3626a309e5e8bd SQL_PLAN_9sdj6nc4ybu5x96fd8705 MANUAL-LOAD YES YES NO
--3.drop bad plan_name
SQL> exec :temp := dbms_spm.drop_sql_plan_baseline(sql_handle => 'SQL_9c3626a309e5e8bd', plan_name => 'SQL_PLAN_9sdj6nc4ybu5x96fd8705');
PL/SQL procedure successfully completed.
SQL> select sql_handle, plan_name, origin, enabled, accepted, fixed from dba_sql_plan_baselines;
SQL_HANDLE PLAN_NAME ORIGIN ENA ACC FIX
------------------------------ ------------------------------ -------------- --- --- ---
SQL_9c3626a309e5e8bd SQL_PLAN_9sdj6nc4ybu5x2b78d17a MANUAL-LOAD YES YES NO
验证稳固执行计划的效果：
SQL> select /*+ no_index(a idx_emp_empno) no_index(b idx_dept_deptno)*/a.empno, a.ename, b.dname, a.job, a.sal from emp a, dept b where a.deptno = b.deptno and empno = 7788;
EMPNO ENAME DNAME JOB SAL
---------- ---------- -------------- --------- ----------
7788 SCOTT RESEARCH ANALYST 3000
SQL> select * from table(dbms_xplan.display_cursor(null,null,'allstats last'));
PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
SQL_ID dqd10y7wqrg7f, child number 1
-------------------------------------
select /*+ no_index(a idx_emp_empno) no_index(b
idx_dept_deptno)*/a.empno, a.ename, b.dname, a.job, a.sal from emp a,
dept b where a.deptno = b.deptno and empno = 7788
Plan hash value: 1725450077
-----------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers |
-----------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | 1 |00:00:00.01 | 6 |
| 1 | NESTED LOOPS | | 1 | 1 | 1 |00:00:00.01 | 6 |
| 2 | NESTED LOOPS | | 1 | 1 | 1 |00:00:00.01 | 5 |
| 3 | TABLE ACCESS BY INDEX ROWID| EMP | 1 | 1 | 1 |00:00:00.01 | 3 |
|* 4 | INDEX RANGE SCAN | IDX_EMP_EMPNO | 1 | 1 | 1 |00:00:00.01 | 2 |
|* 5 | INDEX RANGE SCAN | IDX_DEPT_DEPTNO | 1 | 1 | 1 |00:00:00.01 | 2 |
| 6 | TABLE ACCESS BY INDEX ROWID | DEPT | 1 | 1 | 1 |00:00:00.01 | 1 |
-----------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
4 - access("EMPNO"=7788)
5 - access("A"."DEPTNO"="B"."DEPTNO")
Note
-----
- SQL plan baseline SQL_PLAN_9sdj6nc4ybu5x2b78d17a used for this statement
可以看到SPM已经起作用了。但如果谓词条件换成7900，就会不起作用。我没有找到SPM中类似像sql_profile中force_match的参数，日常工作中也是使用sql_profile稳固执行计划多一些。
另外注意dba_sql_plan_baselines中记录的执行计划对应的ACCEPTED和ENABLE的值都为YES，才可能会被SQL使用。
常用操作：
select sql_handle, plan_name, origin, enabled, accepted, fixed from dba_sql_plan_baselines;
1)将ENABLE的值设为"YES" or "NO"
var temp number
exec :temp := dbms_spm.alter_sql_plan_baseline(sql_handle => 'SQL_9c3626a309e5e8bd', plan_name => 'SQL_PLAN_9sdj6nc4ybu5x96fd8705', attribute_name => 'ENABLED', attribute_value => 'YES');
var temp number
exec :temp := dbms_spm.alter_sql_plan_baseline(sql_handle => 'SQL_9c3626a309e5e8bd', plan_name => 'SQL_PLAN_9sdj6nc4ybu5x96fd8705', attribute_name => 'ENABLED', attribute_value => 'NO');
2)将ACCEPTED值设为"YES"
var temp clob
exec :temp := dbms_spm.evolve_sql_plan_baseline(sql_handle => 'SQL_9c3626a309e5e8bd', plan_name => 'SQL_PLAN_9sdj6nc4ybu5x96fd8705', verify => 'NO', commit => 'YES');
注：我这里测试(在11.2.0.4环境下)发现ACCEPTED值设为"YES"后，无法再设置成"NO"，而ENABLED的值可以自由设置为"YES" or "NO"。
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