自动创建SQL_profile 改变和稳定 SQL 执行计划

SQL> create table t1 as select object_id,object_name from dba_objects where rownum<=50000;

SQL> create table t2 as select * from dba_objects;

SQL> create index t2_idx on t2(object_id);

SQL> exec dbms_stats.gather_table_stats(user,'t1',cascade=>true,method_opt=>'for all columns size 1');

SQL> exec dbms_stats.gather_table_stats(user,'t2',cascade=>true,method_opt=>'for all columns size 1');

---对这条SQL 进行创建SQL_profile
SQL> select t1.*,t2.owner from t1,t2 where t1.object_name like '%T1%' and t1.object_id=t2.object_id;

SQL> select * from table(dbms_xplan.display_cursor);

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
SQL_ID 4zbqykx89yc8v, child number 0
-------------------------------------
select t1.*,t2.owner from t1,t2 where t1.object_name like '%T1%' and
t1.object_id=t2.object_id

Plan hash value: 1838229974

---------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
---------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | | | 210 (100)| |

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
|* 1 | HASH JOIN | | 2500 | 97K| 210 (2)| 00:00:03 |
|* 2 | TABLE ACCESS FULL| T1 | 2500 | 72500 | 54 (2)| 00:00:01 |
| 3 | TABLE ACCESS FULL| T2 | 50605 | 543K| 155 (1)| 00:00:02 |
---------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

1 - access("T1"."OBJECT_ID"="T2"."OBJECT_ID")
2 - filter("T1"."OBJECT_NAME" LIKE '%T1%')

22 rows selected.

---创建sql_profile
SQL> var tuning_task varchar2(1000);

SQL> DECLARE
l_sql_id v$session.prev_sql_id%TYPE;
l_tuning_task VARCHAR2(30);
BEGIN
l_sql_id:='4zbqykx89yc8v';
l_tuning_task := dbms_sqltune.create_tuning_task(sql_id => l_sql_id);
:tuning_task:=l_tuning_task;
dbms_sqltune.execute_tuning_task(l_tuning_task);
dbms_output.put_line(l_tuning_task);
END;
/

PL/SQL procedure successfully completed.

SQL> print tuning_task;

TUNING_TASK
--------------------------------------------------------------------------------
TASK_179

SQL> SELECT dbms_sqltune.report_tuning_task('TASK_179') FROM dual;

GENERAL INFORMATION SECTION
-------------------------------------------------------------------------------
Tuning Task Name : TASK_179
Tuning Task Owner : CQWR
Scope : COMPREHENSIVE
Time Limit(seconds) : 1800
Completion Status : COMPLETED
Started at : 12/29/2014 09:58:05
Completed at : 12/29/2014 09:58:05
Number of SQL Profile Findings : 1

-------------------------------------------------------------------------------
Schema Name: CQWR
SQL ID : 4zbqykx89yc8v
SQL Text : select t1.*,t2.owner from t1,t2 where t1.object_name like '%T1%'
and t1.object_id=t2.object_id

-------------------------------------------------------------------------------
FINDINGS SECTION (1 finding)
-------------------------------------------------------------------------------

1- SQL Profile Finding (see explain plans section below)
--------------------------------------------------------
A potentially better execution plan was found for this statement.
为此语句找到了性能
Recommendation (estimated benefit: 52.34%)
------------------------------------------
-考虑接受推荐的 SQL
- Consider accepting the recommended SQL profile.
execute dbms_sqltune.accept_sql_profile(task_name => 'TASK_179', replace
=> TRUE);

-------------------------------------------------------------------------------
EXPLAIN PLANS SECTION
-------------------------------------------------------------------------------

1- Original With Adjusted Cost
------------------------------
Plan hash value: 1838229974

---------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
---------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 23 | 920 | 210 (2)| 00:00:03 |
|* 1 | HASH JOIN | | 23 | 920 | 210 (2)| 00:00:03 |
|* 2 | TABLE ACCESS FULL| T1 | 23 | 667 | 54 (2)| 00:00:01 |
| 3 | TABLE ACCESS FULL| T2 | 50605 | 543K| 155 (1)| 00:00:02 |
---------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

1 - access("T1"."OBJECT_ID"="T2"."OBJECT_ID")
2 - filter("T1"."OBJECT_NAME" LIKE '%T1%')

2- Using SQL Profile
--------------------
Plan hash value: 3787413387

--------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 23 | 920 | 100 (1)| 00:00:02 |
| 1 | TABLE ACCESS BY INDEX ROWID| T2 | 1 | 11 | 2 (0)| 00:00:01 |
| 2 | NESTED LOOPS | | 23 | 920 | 100 (1)| 00:00:02 |
|* 3 | TABLE ACCESS FULL | T1 | 23 | 667 | 54 (2)| 00:00:01 |
|* 4 | INDEX RANGE SCAN | T2_IDX | 1 | | 1 (0)| 00:00:01 |
--------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

3 - filter("T1"."OBJECT_NAME" LIKE '%T1%')
4 - access("T1"."OBJECT_ID"="T2"."OBJECT_ID")

-------------------------------------------------------------------------------

接受这个SQL Profile
SQL> execute dbms_sqltune.accept_sql_profile(task_name => 'TASK_179', replace=> TRUE ,force_match=>true);

--查看 已存在的 SQL Profile
SQL> select name,category,signature,type,status,force_matching from dba_sql_profiles;

SQL>--删除SQL Profile
exec dbms_sqltune.drop_sql_profile('SYS_SQLPROF_014b39f084c88000');

结论：对SQL语句，去掉重复的空格（不包括字符常量），将大小写转换成相同，比如均为大写（不包括字符常量）后，
如果SQL相同，那么SQL语句的exact_matching_signature就是相同的。
对SQL语句，去掉重复的空格（不包括字符常量），
将大小写转换成相同，比如均为大写（不包括字符常量），然后去掉SQL中的常量，如果SQL相同，
那么SQL语句的force_matching_signature就是相同的。
但是例外的情况是：如果SQL中有绑定变量，force_matching_signature
就会与exact_matching_signature一样的生成标准。

来自为知笔记(Wiz)