ORACLE 11G SPM(SQL PLAN manager)浅析

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。

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_planNAME                                 TYPE        VALUE------------------------------------ ----------- ------------------------------optimizer_capture_sql_plan_baselines boolean     FALSEoptimizer_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_ACCESS16 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 108Plan 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 108Plan 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 108SYS_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 108Plan 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 2469ORA-06512: 在 line 1temp---------

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 completedtemp----------------------------------------------------------------------------------------                        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     = YESPlan: 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 108SYS_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 completedtemp---------1SQL> 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 108SYS_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 108Plan 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 whereobject_id=4Plan 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 completedtemp---------1SQL> 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 whereobject_id=4Plan 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 completedtemp---------1SQL> 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=4SYS_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 completedtemp---------1SQL>  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 whereobject_id=4Plan 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。