有助于保持sql的语句特性，只允许执行性能提高的执行计划。
它不同于stored outlines， spm在于稳定sql性能，而store outlines在于冻结sql执行计划
事列
1.启用optimizer_cature_sql_plan_baselines 捕获sql语句
SQL> alter session set optimizer_capture_sql_plan_baselines = true;
Session altered.
SQL> select * from objs where object_id = 2;
no rows selected
SQL> select * from objs where object_id = 2;
no rows selected
SQL> alter session set optimizer_capture_sql_plan_baselines = false;
Session altered.
2.查询dba_sql_plan_baselines，确定sql的spm状态
SQL> select plan_name, sql_handle, enabled, accepted, fixed,
2 module, sql_text
3 from dba_sql_plan_baselines;
PLAN_NAME SQL_HANDLE ENABLED ACCEPTED FIXED MODULE SQL_TEXT
------------------------------ -------------------- --------- --------- --------- -------------------- --------------------------------------------------
SQL_PLAN_4pzq3z6xcqkpwd0984253 SQL_4afec3f9bacb4abc YES YES NO SQL*Plus select * from objs where object_id = 2
3.增加索引改变环境再运行sql
SQL> alter session set optimizer_capture_sql_plan_baselines = true;
Session altered.
SQL> select * from objs where object_id = 2;
no rows selected
SQL> select * from objs where object_id = 2;
no rows selected
SQL> alter session set optimizer_capture_sql_plan_baselines = false;
Session altered.
4.查询dba_sql_plan_baselines
SQL> select plan_name, sql_handle, enabled, accepted, fixed, module, sql_text from dba_sql_plan_baselines;
PLAN_NAME SQL_HANDLE ENABLED ACCEPTED FIXED MODULE SQL_TEXT
------------------------------ -------------------- --------- --------- --------- -------------------- --------------------------------------------------
SQL_PLAN_4pzq3z6xcqkpwbe4c314c SQL_4afec3f9bacb4abc YES NO NO SQL*Plus select * from objs where object_id = 2
SQL_PLAN_4pzq3z6xcqkpwd0984253 SQL_4afec3f9bacb4abc YES YES NO SQL*Plus select * from objs where object_id = 2
SQL>
5.测试
SQL>
SQL> set autotrace on
SQL> select * from objs where object_id = 2;
no rows selected
Execution Plan
----------------------------------------------------------
Plan hash value: 954894094
--------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 98 | 247 (1)| 00:00:03 |
|* 1 | TABLE ACCESS FULL| OBJS | 1 | 98 | 247 (1)| 00:00:03 |
--------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter("OBJECT_ID"=2)
Note
-----
- SQL plan baseline "SQL_PLAN_4pzq3z6xcqkpwd0984253" used for this statement
Statistics
----------------------------------------------------------
255 recursive calls
0 db block gets
1044 consistent gets
879 physical reads
0 redo size
1343 bytes sent via SQL*Net to client
513 bytes received via SQL*Net from client
1 SQL*Net roundtrips to/from client
28 sorts (memory)
0 sorts (disk)
0 rows processed
SQL> alter session set optimizer_use_sql_plan_baselines = false;
Session altered.
SQL> select * from objs where object_id = 2;
no rows selected
Execution Plan
----------------------------------------------------------
Plan hash value: 613004408
-----------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
-----------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 98 | 2 (0)| 00:00:01 |
| 1 | TABLE ACCESS BY INDEX ROWID| OBJS | 1 | 98 | 2 (0)| 00:00:01 |
|* 2 | INDEX RANGE SCAN | IDX_OBJSID_OBJS | 1 | | 1 (0)| 00:00:01 |
-----------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
2 - access("OBJECT_ID"=2)
Statistics
----------------------------------------------------------
1 recursive calls
0 db block gets
2 consistent gets
4 physical reads
0 redo size
1343 bytes sent via SQL*Net to client
513 bytes received via SQL*Net from client
1 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
0 rows processed
可以看到当启动optimizer_user_sql_plan_baselines时走索引应该是最优的却没有使用
plan_name accecpt 为 no 影响了走索引计划