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11g推出的SPM是一种主动的稳定执行计划的手段，能够保证只有被验证过的执行计划才会被启用。SPM既能够主动的稳定执行计划，又保留了继续使用新的执行效率更高的执行计划的机会。
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启用SPM后，每一个SQL都会存在对应的SQL PLAN Baseline，存储在DBA_SQL_PLAN_BASELINES视图。
该视图的enable和accept列均为YES的SQL PLAN Baseline所对应的执行计划才会被执行。如果有超过1个以上的均为YES，那么oracle会选择其中cost值最小的为执行计划。
可以有2种方法产生SQL PLAN Baseline
1.自动捕获
2.手动生成/批量导入
下面先介绍自动捕获。参数optimizer_capture_sql_plan_baselines用于控制是否开启自动捕获，默认为false。参数optimizer_use_sql_plan_baselines用于控制是否启用SPM，默认为TRUE，表示默认情况下Oracle在生成执行计划时就会启用SPM，使用已有的SQL PLAN Baseline。
创建一个自动捕获SQL PLAN Baseline，并据此来稳定执行计划。
默认参数
sys@TEST:test> show parameter sql_plan NAME TYPE VALUE ------------------------------------ ----------- ------------------------------ optimizer_capture_sql_plan_baselines boolean FALSE optimizer_use_sql_plan_baselines boolean TRUE
在当前session禁用SPM,同时开启自动捕获。
aaa@TEST:test> alter session set optimizer_capture_sql_plan_baselines=true; Session altered. aaa@TEST:test> alter session set optimizer_use_sql_plan_baselines=false; Session altered.
创建测试表T2，并创建索引
aaa@TEST:test> create table t2 as select * from dba_objects; Table created. aaa@TEST:test> create index idx_t2 on t2(object_id); Index created.
对T2收集统计信息
aaa@TEST:test> exec dbms_stats.gather_table_stats(ownname => 'AAA',tabname => 'T2',estimate_percent => 100,cascade => true); PL/SQL procedure successfully completed.
执行SQL
aaa@TEST:test> select object_id,object_name from t2 where object_id between 103 and 108; OBJECT_ID OBJECT_NAME ---------- ------------------------------ 103 MIGRATE$ 104 DEPENDENCY$ 105 ACCESS$ 106 I_DEPENDENCY1 107 I_DEPENDENCY2 108 I_ACCESS1 6 rows selected.
执行计划如下
----------------------------------------------------------------------------------------------------------------------------------- SQL_ID 8vtdn0kgytfxr, child number 0 ------------------------------------- select object_id,object_name from t2 where object_id between 103 and 108 Plan hash value: 2008370210 -------------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | -------------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | | | 3 (100)| | | 1 | TABLE ACCESS BY INDEX ROWID| T2 | 6 | 180 | 3 (0)| 00:00:01 | |* 2 | INDEX RANGE SCAN | IDX_T2 | 6 | | 2 (0)| 00:00:01
因为该SQL只执行过一次，所以Oracle不会自动捕获其SQL PLAN Baseline，验证：
aaa@TEST:test> select sql_handle,plan_name,origin,enabled,accepted,sql_text from dba_sql_plan_baselines where sql_text like 'select object_id%'; no rows selected
再执行一次，执行计划没有变化，因为SQL已经重复执行，Oracle会自动捕获其SQL PLAN Baseline
SQL> select sql_handle,plan_name,origin,enabled,accepted,sql_text from dba_sql_plan_baselines where sql_text like 'select object_id%'; SQL_HANDLE PLAN_NAME ORIGIN ENABLED ACCEPTED SQL_TEXT ------------------------------ ------------------------------ -------------- ------- -------- -------------------------------------------------------------------------------- SYS_SQL_ac526b1e4be74880 SQL_PLAN_asnmb3t5yfk4024c6dbb6 AUTO-CAPTURE YES YES select object_id,object_name from t2 where object_id between 103 and 108
这里修改索引IDX_T2的聚簇因子修改为2400万，改变目标SQL的执行计划为全表。
SQL> exec dbms_stats.set_index_stats(ownname=>'AAA',indname=>'IDX_T2',clstfct=>24000000,no_invalidate => false); PL/SQL procedure successfully completed
重新执行SQL，执行计划如下，为全表
select object_id,object_name from t2 where object_id between 103 and 108 Plan hash value: 1513984157 -------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | -------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | | | 290 (100)| | |* 1 | TABLE ACCESS FULL| T2 | 6 | 180 | 290 (1)| 00:00:04 | --------------------------------------------------------------------------
因为目标SQL已经重复执行且又产生了一个执行计划，所以Oracle会自动捕获并创建这个新的执行计划所对应的SQL PLAN Baseline，查询视图
SQL> select sql_handle,plan_name,origin,enabled,accepted,sql_text from dba_sql_plan_baselines where sql_text like 'select object_id%'; SQL_HANDLE PLAN_NAME ORIGIN ENABLED ACCEPTED SQL_TEXT ------------------------------ ------------------------------ -------------- ------- -------- -------------------------------------------------------------------------------- SYS_SQL_ac526b1e4be74880 SQL_PLAN_asnmb3t5yfk4024c6dbb6 AUTO-CAPTURE YES YES select object_id,object_name from t2 where object_id between 103 and 108 SYS_SQL_ac526b1e4be74880 SQL_PLAN_asnmb3t5yfk40b860bcf2 AUTO-CAPTURE YES NO select object_id,object_name from t2 where object_id between 103 and 108
然后关闭当前session自动捕获SQL PLAN Baseline，并启用SPM，就是恢复11g默认
aaa@TEST:test> alter session set optimizer_capture_sql_plan_baselines=false; Session altered. aaa@TEST:test> alter session set optimizer_use_sql_plan_baselines=true; Session altered.
现在索引IDX_T2的聚簇因子还是2400万
aaa@TEST:test> select index_name,clustering_factor from user_indexes; INDEX_NAME CLUSTERING_FACTOR ------------------------------ ----------------- IDX_T2 24000000
再次执行目标SQL，其执行计划
PLAN_TABLE_OUTPUT ----------------------------------------------------------------------------------------------------------------------------------- SQL_ID 8vtdn0kgytfxr, child number 2 ------------------------------------- select object_id,object_name from t2 where object_id between 103 and 108 Plan hash value: 2008370210 -------------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | -------------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | | | 2069 (100)| | | 1 | TABLE ACCESS BY INDEX ROWID| T2 | 6 | 180 | 2069 (0)| 00:00:25 | |* 2 | INDEX RANGE SCAN | IDX_T2 | 6 | | 2 (0)| 00:00:01 | -------------------------------------------------------------------------------------- Note ----- - SQL plan baseline SQL_PLAN_asnmb3t5yfk4024c6dbb6 used for this statement
上述可以看出，现在目标SQL的执行计划已经从对表的全表扫描，变成了索引范围扫描。并且NOTE下面有“SQL plan baseline SQL_PLAN_asnmb3t5yfk4024c6dbb6 used for this statement”，这表明在启用SPM情况下， 即使目标SQL产生了新执行计划，Oracle依然只会使用enabled和accepted均为YES的SQL PLAN Baseline对应的执行计划。
如果想启用新的执行计划，对于不同版本操作不一样。
11gR1，只需要将目标SQL锁采用的名为SQL_PLAN_asnmb3t5yfk4024c6dbb6的SQL PLAN Baseline的accepted值变为NO即可。
SQL> var temp number; SQL> exec :temp:=dbms_spm.alter_sql_plan_baseline(sql_handle => 'SYS_SQL_ac526b1e4be74880',plan_name => 'SQL_PLAN_asnmb3t5yfk4024c6dbb6',attribute_name => 'accepted',attribute_value => 'NO');
在11gR2中，执行上述代码或报错
SQL> var temp number; SQL> exec :temp:=dbms_spm.alter_sql_plan_baseline(sql_handle => 'SYS_SQL_ac526b1e4be74880',plan_name => 'SQL_PLAN_asnmb3t5yfk4024c6dbb6',attribute_name => 'accepted',attribute_value => 'NO'); begin :temp:=dbms_spm.alter_sql_plan_baseline(sql_handle => 'SYS_SQL_ac526b1e4be74880',plan_name => 'SQL_PLAN_asnmb3t5yfk4024c6dbb6',attribute_name => 'accepted',attribute_value => 'NO'); end; ORA-38136: 指定的属性名 ACCEPTED 无效 ORA-06512: 在 "SYS.DBMS_SPM", line 2469 ORA-06512: 在 line 1 temp ---------
在11gR2中，使用dbms_spm.evolve_sql_plan_baseline和dbms_spm.alter_sql_plan_baseline达到启用新执行计划的目的。
先用dbms_spm.evolve_sql_plan_baseline将新执行计划的accepted置为YES
SQL> var temp varchar2(4000); SQL> exec :temp:=dbms_spm.evolve_sql_plan_baseline(sql_handle => 'SYS_SQL_ac526b1e4be74880',plan_name => 'SQL_PLAN_asnmb3t5yfk40b860bcf2',verify => 'NO',commit => 'YES'); PL/SQL procedure successfully completed temp --------- ------------------------------------------------------------------------------- Evolve SQL Plan Baseline Report ------------------------------------------------------------------------------- Inputs: ------- SQL_HANDLE = SYS_SQL_ac526b1e4be74880 PLAN_NAME = SQL_PLAN_asnmb3t5yfk40b860bcf2 TIME_LIMIT = DBMS_SPM.AUTO_LIMIT VERIFY = NO COMMIT = YES Plan: SQL_PLAN_asnmb3t5yfk40b860bcf2 ------------------------------------ It is already an accepted plan. ------------------------------------------------------------------------------- Report Summary ------------------------------------------------------------------------------- There were no SQL plan baselines that required processing. SQL> select sql_handle,plan_name,origin,enabled,accepted,sql_text from dba_sql_plan_baselines where sql_text like 'select object_id%'; SQL_HANDLE PLAN_NAME ORIGIN ENABLED ACCEPTED SQL_TEXT ------------------------------ ------------------------------ -------------- ------- -------- -------------------------------------------------------------------------------- SYS_SQL_ac526b1e4be74880 SQL_PLAN_asnmb3t5yfk4024c6dbb6 AUTO-CAPTURE YES YES select object_id,object_name from t2 where object_id between 103 and 108 SYS_SQL_ac526b1e4be74880 SQL_PLAN_asnmb3t5yfk40b860bcf2 AUTO-CAPTURE YES YES select object_id,object_name from t2 where ob
再使用dbms_spm.alter_sql_plan_baseline把PLAN_NAME为SQL_PLAN_asnmb3t5yfk4024c6dbb6的SQL PLAN Baseline的enabled置为NO。
SQL> var temp number; SQL> exec :temp:=dbms_spm.alter_sql_plan_baseline(sql_handle => 'SYS_SQL_ac526b1e4be74880',plan_name => 'SQL_PLAN_asnmb3t5yfk4024c6dbb6',attribute_name => 'ENABLED',attribute_value => 'NO'); PL/SQL procedure successfully completed temp --------- 1 SQL> select sql_handle,plan_name,origin,enabled,accepted,sql_text from dba_sql_plan_baselines where sql_text like 'select object_id%'; SQL_HANDLE PLAN_NAME ORIGIN ENABLED ACCEPTED SQL_TEXT ------------------------------ ------------------------------ -------------- ------- -------- -------------------------------------------------------------------------------- SYS_SQL_ac526b1e4be74880 SQL_PLAN_asnmb3t5yfk4024c6dbb6 AUTO-CAPTURE NO YES select object_id,object_name from t2 where object_id between 103 and 108 SYS_SQL_ac526b1e4be74880 SQL_PLAN_asnmb3t5yfk40b860bcf2 AUTO-CAPTURE YES YES select object_id,object_name from t2 where object_id between 103 and 108
再次执行目标SQL
PLAN_TABLE_OUTPUT ----------------------------------------------------------------------------------------------------------------------------------- SQL_ID 8vtdn0kgytfxr, child number 0 ------------------------------------- select object_id,object_name from t2 where object_id between 103 and 108 Plan hash value: 1513984157 -------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | -------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | | | 290 (100)| | |* 1 | TABLE ACCESS FULL| T2 | 6 | 180 | 290 (1)| 00:00:04 | -------------------------------------------------------------------------- Note ----- - SQL plan baseline SQL_PLAN_asnmb3t5yfk40b860bcf2 used for this statement
使用了新的执行计划，注意NOTE中SQL_PLAN_asnmb3t5yfk40b860bcf2即SQL PLAN Baseline中enabled和accepted均为YES的SQL PLAN Baseline对应的执行执行计划名。
从测试结果看出，我们可以在目标SQL的多个执行计划之间切换，所以SPM既能稳定执行计划，又保留了继续使用新的执行计划的机会。
接下来介绍手工生成SQL PLAN Baseline。手工生成很简单，核心是调用dbms_spm.load_plans_from_cursor_cache。
针对目标SQL使用dbms_spm.load_plans_from_cursor_cache手工生成其初始执行计划所对应的SQL PLAN Baseline。
PLAN_TABLE_OUTPUT ----------------------------------------------------------------------------------------------------------------------------------- SQL_ID 85htp4tya3uwm, child number 0 ------------------------------------- select /*+ no_index(t2 idx_t2)*/ object_name,object_id from t2 where object_id=4 Plan hash value: 1513984157 -------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | -------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | | | 290 (100)| | |* 1 | TABLE ACCESS FULL| T2 | 1 | 30 | 290 (1)| 00:00:04 |
上述SQL的SQL_ID为85htp4tya3uwm，plan_hash_value为1513984157，现在没有开启自动捕获SQL PLAN Baseline。视图dba_sql_plan_baselines应该没有对应信息。
select sql_handle,plan_name,origin,enabled,accepted,sql_text from dba_sql_plan_baselines where sql_text like 'select object_name%'; SQL_HANDLE PLAN_NAME ORIGIN ENABLED ACCEPTED SQL_TEXT ------------------------------ ------------------------------ -------------- ------- -------- -----------------------------------------------------------
使用目标SQL的SQL_ID和PLAN_HASH_VALUE来生成所对应的SQL PLAN Baseline。
SQL> var temp number; SQL> exec :temp:=dbms_spm.load_plans_from_cursor_cache(sql_id=>'85htp4tya3uwm',plan_hash_value=>1513984157); PL/SQL procedure successfully completed temp --------- 1 SQL> select sql_handle,plan_name,origin,enabled,accepted,sql_text from dba_sql_plan_baselines where sql_text like 'select /*+ no_index(t2 idx_t2)*/ object_name%'; SQL_HANDLE PLAN_NAME ORIGIN ENABLED ACCEPTED SQL_TEXT ------------------------------ ------------------------------ -------------- ------- -------- -------------------------------------------------------------------------------- SYS_SQL_75b06ae056223f5f SQL_PLAN_7bc3aw1b24guzb860bcf2 MANUAL-LOAD YES YES select /*+ no_index(t2 idx_t2)*/ object_name,object_id from t2 where object_id=4
已经生成了SQL_HANDLE为SYS_SQL_75b06ae056223f5f和PLAN_NAME为SQL_PLAN_7bc3aw1b24guzb860bcf2的SQL PLAN Baseline。
改写原目标SQL，加入强制走索引hint
PLAN_TABLE_OUTPUT ----------------------------------------------------------------------------------------------------------------------------------- SQL_ID 0argb4cn0sybz, child number 0 ------------------------------------- select /*+ index(t2 idx_t2)*/ object_name,object_id from t2 where object_id=4 Plan hash value: 2008370210 -------------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | -------------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | | | 332 (100)| | | 1 | TABLE ACCESS BY INDEX ROWID| T2 | 1 | 30 | 332 (0)| 00:00:04 | |* 2 | INDEX RANGE SCAN | IDX_T2 | 1 | | 1 (0)| 00:00:01 |
改写后走索引，SQL_ID=0argb4cn0sybz，Plan hash value: 2008370210。
再加上原目标SQL的SQL_HANDLE来生成新的SQL PLAN Baseline。
SQL> exec :temp:=dbms_spm.load_plans_from_cursor_cache(sql_id=>'0argb4cn0sybz',plan_hash_value=>2008370210,sql_handle=>'SYS_SQL_75b06ae056223f5f'); PL/SQL procedure successfully completed temp --------- 1 SQL> select sql_handle,plan_name,origin,enabled,accepted,sql_text from dba_sql_plan_baselines where sql_text like 'select /*+ no_index(t2 idx_t2)*/ object_name%'; SQL_HANDLE PLAN_NAME ORIGIN ENABLED ACCEPTED SQL_TEXT ------------------------------ ------------------------------ -------------- ------- -------- -------------------------------------------------------------------------------- SYS_SQL_75b06ae056223f5f SQL_PLAN_7bc3aw1b24guz24c6dbb6 MANUAL-LOAD YES YES select /*+ no_index(t2 idx_t2)*/ object_name,object_id from t2 where object_id=4 SYS_SQL_75b06ae056223f5f SQL_PLAN_7bc3aw1b24guzb860bcf2 MANUAL-LOAD YES YES select /*+ no_index(t2 idx_t2)*/ object_name,object_id from t2 where object_id=4
上述可以看出原目标SQL生成了新的PLAN，其PLAN_NAME为SQL_PLAN_7bc3aw1b24guz24c6dbb6。注意新生成的SQL PLAN Baseline的enabled和accepted均为YES，这是个自动捕获不同的地方。
现在DROP掉原目标SQL走全表扫描所对应的SQL PLAN Baseline。
SQL> exec :temp:=dbms_spm.drop_sql_plan_baseline(sql_handle =>'SYS_SQL_75b06ae056223f5f',plan_name => 'SQL_PLAN_7bc3aw1b24guzb860bcf2'); PL/SQL procedure successfully completed temp --------- 1 SQL> select sql_handle,plan_name,origin,enabled,accepted,sql_text from dba_sql_plan_baselines where sql_text like 'select /*+ no_index(t2 idx_t2)*/ object_name%'; SQL_HANDLE PLAN_NAME ORIGIN ENABLED ACCEPTED SQL_TEXT ------------------------------ ------------------------------ -------------- ------- -------- -------------------------------------------------------------------------------- SYS_SQL_75b06ae056223f5f SQL_PLAN_7bc3aw1b24guz24c6dbb6 MANUAL-LOAD YES YES select /*+ no_index(t2 idx_t2)*/ object_name,object_id from t2 where object_id=4
再次执行原SQL，可以看到走了索引
PLAN_TABLE_OUTPUT ----------------------------------------------------------------------------------------------------------------------------------- SQL_ID 85htp4tya3uwm, child number 2 ------------------------------------- select /*+ no_index(t2 idx_t2)*/ object_name,object_id from t2 where object_id=4 Plan hash value: 2008370210 -------------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | -------------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | | | 332 (100)| | | 1 | TABLE ACCESS BY INDEX ROWID| T2 | 1 | 30 | 332 (0)| 00:00:04 | |* 2 | INDEX RANGE SCAN | IDX_T2 | 1 | | 1 (0)| 00:00:01 | -------------------------------------------------------------------------------------- Note ----- - SQL plan baseline SQL_PLAN_7bc3aw1b24guz24c6dbb6 used for this statement
最后注意NOTE下面，使用了SQL PLAN Baeline。
