oracle 如何稳定执行计划
2.5.1 automatic sql profile 调整执行计划
适合sql无法改写或验证改写是否成功的情况
验证：
Oracel 账号SYS
Conn /as sysdba;
1> create table t1(n number);
2> declare
begin
for i in 1 ..10000
loop
insert into t1 values(i);
commit;
end loop;
end;
/
3> select count(*) from t1;
4> create index idx_t1 on t1(n);
5> exec dbms_stats.gather_table_stats(ownname=>'SYS',tabname=>'T1',method_opt=>'for all columns size 1',cascade=>true);
6> select /*+ no_index(t1 idx_t1) */ * from t1 where n=1;
7> select * from table(dbms_xplan.display_cursor(null,null,'advanced'));
8> declare
my_task_name varchar2(30);
my_sqltext clob;
begin
my_sqltext := 'select /*+ no_index(t1 idx_t1) */ * from t1 where n=1';
my_task_name := dbms_sqltune.create_tuning_task(
sql_text => my_sqltext,
user_name => 'SYS',
scope => 'COMPREHENSIVE',
time_limit => 60,
task_name => 'my_sql_tuning_task_2 ',
description => ' Task to rune a query on table t1 ');
end;
/
9> begin
dbms_sqltune.execute_tuning_task( task_name => 'my_sql_tuning_task_2 ');
end;
/
10>
SQL> set long 9000
SQL> set longchunksize 1000
SQL> set linesize 800
SQL> select dbms_sqltune.report_tuning_task( 'my_sql_tuning_task_2 ') from dual;
GENERAL INFORMATION SECTION
-------------------------------------------------------------------------------
Tuning Task Name : my_sql_tuning_task_2
Tuning Task Owner : SYS
Workload Type : Single SQL Statement
Execution Count : 2
Current Execution : EXEC_277
Execution Type : TUNE SQL
Scope : COMPREHENSIVE
Time Limit(seconds): 60
Completion Status : COMPLETED
Started at : 04/17/2016 12:09:37
Completed at : 04/17/2016 12:09:37
-------------------------------------------------------------------------------
Schema Name: SYS
SQL ID : 4bh6sn1zvpgq7
SQL Text : select /*+ no_index(t1 idx_t1) */ * from t1 where n=1
-------------------------------------------------------------------------------
FINDINGS SECTION (1 finding)
-------------------------------------------------------------------------------
1- SQL Profile Finding (see explain plans section below)
--------------------------------------------------------
为此语句找到了性能更好的执行计划。
Recommendation (estimated benefit: 95%)
---------------------------------------
- 考虑接受推荐的 SQL 概要文件。
execute dbms_sqltune.accept_sql_profile(task_name =>
'my_sql_tuning_task_2 ', task_owner => 'SYS', replace => TRUE);
Validation results
------------------
已对 SQL profile 进行测试, 方法为执行其计划和原始计划并测量与计划相对应的执行统计信息。如果其中一个计划运行在很短的时间内就完成,
则另一计划可能只执行了一部分。
Original Plan With SQL Profile % Improved
------------- ---------------- ----------
Completion Status: COMPLETE COMPLETE
Elapsed Time(us): 597 68 88.6 %
CPU Time(us): 0 0
User I/O Time(us): 0 0
Buffer Gets: 20 1 95 %
Physical Read Requests: 0 0
Physical Write Requests: 0 0
Physical Read Bytes: 0 0
Physical Write Bytes: 0 0
Rows Processed: 1 1
Fetches: 1 1
Executions: 1 1
Notes
-----
1. original plan 已首先执行以预热缓冲区高速缓存。
2. original plan 的统计信息是后面的 9 执行的平均值。
3. SQL profile plan 已首先执行以预热缓冲区高速缓存。
4. the SQL profile plan 的统计信息是后面的 9 执行的平均值。
-------------------------------------------------------------------------------
EXPLAIN PLANS SECTION
-------------------------------------------------------------------------------
1- Original With Adjusted Cost
------------------------------
Plan hash value: 3617692013
--------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 4 | 7 (0)| 00:00:01 |
|* 1 | TABLE ACCESS FULL| T1 | 1 | 4 | 7 (0)| 00:00:01 |
--------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter("N"=1)
2- Using SQL Profile
--------------------
Plan hash value: 1369807930
---------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
---------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 4 | 1 (0)| 00:00:01 |
|* 1 | INDEX RANGE SCAN| IDX_T1 | 1 | 4 | 1 (0)| 00:00:01 |
---------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - access("N"=1)
-------------------------------------------------------------------------------
11> execute dbms_sqltune.accept_sql_profile(task_name => 'my_sql_tuning_task_2 ', task_owner => 'SYS', replace => TRUE);
12> 再次执行 select /*+ no_index(t1 idx_t1) */ * from t1 where n=1;
select * from table(dbms_xplan.display_cursor(null,null,'advanced'));
原来走全表现在走索引范围range扫描了，起到了变更作用，但是，一旦sql参数值或其他变化就会改变这个已调整的automatic sql profile
13> 验证参数值发生改变，又回到全表扫描了
select /*+ no_index(t1 idx_t1) */ * from t1 where n=2;
select * from table(dbms_xplan.display_cursor(null,null,'advanced'));
SQL_ID c4j6hxkqudj1s, child number 0
-------------------------------------
select /*+ no_index(t1 idx_t1) */ * from t1 where n=2
Plan hash value: 3617692013
--------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | | | 7 (100)| |
|* 1 | TABLE ACCESS FULL| T1 | 1 | 4 | 7 (0)| 00:00:01 |
--------------------------------------------------------------------------
Query Block Name / Object Alias (identified by operation id):
-------------------------------------------------------------
1 - SEL$1 / T1@SEL$1
Outline Data
-------------
/*+
BEGIN_OUTLINE_DATA
IGNORE_OPTIM_EMBEDDED_HINTS
OPTIMIZER_FEATURES_ENABLE('11.2.0.1')
DB_VERSION('11.2.0.1')
ALL_ROWS
OUTLINE_LEAF(@"SEL$1")
FULL(@"SEL$1" "T1"@"SEL$1")
END_OUTLINE_DATA
*/
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter("N"=2)
Column Projection Information (identified by operation id):
-----------------------------------------------------------
1 - "N"[NUMBER,22]
14> 让automatic profile 永久生效添加force_match=true，默认force_match=false
execute dbms_sqltune.accept_sql_profile(task_name => 'my_sql_tuning_task_2 ', task_owner => 'SYS', replace => TRUE,force_match=>true);
注意 SYS_SQLPROF_0154228b55fe000是否一样
SQL_ID fd5p89b5jz0ct, child number 0
-------------------------------------
select /*+ no_index(t1 idx_t1) */ * from t1 where n=4
Plan hash value: 1369807930
---------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
---------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | | | 1 (100)| |
|* 1 | INDEX RANGE SCAN| IDX_T1 | 1 | 4 | 1 (0)| 00:00:01 |
---------------------------------------------------------------------------
Query Block Name / Object Alias (identified by operation id):
-------------------------------------------------------------
1 - SEL$1 / T1@SEL$1
Outline Data
-------------
/*+
BEGIN_OUTLINE_DATA
IGNORE_OPTIM_EMBEDDED_HINTS
OPTIMIZER_FEATURES_ENABLE('11.2.0.1')
DB_VERSION('11.2.0.1')
ALL_ROWS
OUTLINE_LEAF(@"SEL$1")
INDEX(@"SEL$1" "T1"@"SEL$1" ("T1"."N"))
END_OUTLINE_DATA
*/
Predicate Information (identified by operation id):
---------------------------------------------------
1 - access("N"=4)
Column Projection Information (identified by operation id):
-----------------------------------------------------------
1 - "N"[NUMBER,22]
Note
-----
- SQL profile SYS_SQLPROF_0154228b55fe0001 used for this statement
已选择46行。
SQL> select /*+ no_index(t1 idx_t1) */ * from t1 where n=5;
N
----------
5
SQL> select * from table(dbms_xplan.display_cursor(null,null,'advanced'));
PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
SQL_ID 6u34k01s3c4rg, child number 0
-------------------------------------
select /*+ no_index(t1 idx_t1) */ * from t1 where n=5
Plan hash value: 1369807930
---------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
---------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | | | 1 (100)| |
|* 1 | INDEX RANGE SCAN| IDX_T1 | 1 | 4 | 1 (0)| 00:00:01 |
---------------------------------------------------------------------------
Query Block Name / Object Alias (identified by operation id):
-------------------------------------------------------------
1 - SEL$1 / T1@SEL$1
Outline Data
-------------
/*+
BEGIN_OUTLINE_DATA
IGNORE_OPTIM_EMBEDDED_HINTS
OPTIMIZER_FEATURES_ENABLE('11.2.0.1')
DB_VERSION('11.2.0.1')
ALL_ROWS
OUTLINE_LEAF(@"SEL$1")
INDEX(@"SEL$1" "T1"@"SEL$1" ("T1"."N"))
END_OUTLINE_DATA
*/
Predicate Information (identified by operation id):
---------------------------------------------------
1 - access("N"=5)
Column Projection Information (identified by operation id):
-----------------------------------------------------------
1 - "N"[NUMBER,22]
Note
-----
- SQL profile SYS_SQLPROF_0154228b55fe0001 used for this statement
已选择46行。