简单讨论在11G，10G中如何稳定SQL执行计划（二）

2022-04-15 04:14:21

在简单讨论在11G，10G中如何稳定SQL执行计划（一）中我们讨论了如何通过SPM中的sql plan baseline 来稳定11G中的执行计划

SPM是11G才有的新特性，那么在11G之前，我们是如何稳定执行计划的？

通过使用SQL PROFILE，关于SQL profile 的原理之类的，如上一篇一样，自己去百度。这里只讨论实际操作

首先，还是模拟出一个SQL对应出两个不同执行计划的情况

具体过程不再赘述，结果如下

SQL> select sql_id,child_number,plan_hash_value,sql_text from v$sql where sql_text like ‘%haha where%‘;  

SQL_ID	      CHILD_NUMBER PLAN_HASH_VALUE
------------- ------------ ---------------
SQL_TEXT
--------------------------------------------------------------------------------
auwza0aq10mk0		 0	3694936490
select * from haha where a=‘10000‘

auwza0aq10mk0		 1	1624320650
select * from haha where a=‘10000‘

通过查看，PLAN_HASH_VALUE为‘3694936490‘的，是走了全表扫描的执行计划，我这里假设走全表扫描是错的！

现在我们假设走索引范围扫描的 ‘1624320650’ 执行计划，是正确的。

环境描述:

现在两个执行计划不同的子cursor，原本正常的时候为走 index range scan，现在突然改走 full table scan，导致sql非常缓慢

现在我们要做的，就是通过sql profile应急对其进行处理

如何处理，我们通过使用一个脚本‘coe_xfr_sql_profile.sql’ 这个脚本可以在MOS的文章 ‘215187.1‘找到

现在我们调用脚本

SQL> @coe_xfr_sql_profile.sql

Parameter 1:
SQL_ID (required)

Enter value for 1: auwza0aq10mk0     ----该脚本第一个输入值，为要绑定执行计划SQL的SQL_ID，这里为auwza0aq10mk0


PLAN_HASH_VALUE AVG_ET_SECS
--------------- -----------
     1624320650        .002
     3694936490        .028

Parameter 2:
PLAN_HASH_VALUE (required)

Enter value for 2: 1624320650        -----选择要绑定的执行计划，这里输入1624320650

Values passed to coe_xfr_sql_profile:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
SQL_ID	       : "auwza0aq10mk0"
PLAN_HASH_VALUE: "1624320650"

SQL>BEGIN
  2    IF :sql_text IS NULL THEN
  3  	 RAISE_APPLICATION_ERROR(-20100, ‘SQL_TEXT for SQL_ID &&sql_id. was not found in memory (gv$sqltext_with_newlines) or AWR (dba_hist_sqltext).‘);
  4    END IF;
  5  END;
  6  /
SQL>SET TERM OFF;
SQL>BEGIN
  2    IF :other_xml IS NULL THEN
  3  	 RAISE_APPLICATION_ERROR(-20101, ‘PLAN for SQL_ID &&sql_id. and PHV &&plan_hash_value. was not found in memory (gv$sql_plan) or AWR (dba_hist_sql_plan).‘);
  4    END IF;
  5  END;
  6  /
SQL>SET TERM OFF;

Execute coe_xfr_sql_profile_auwza0aq10mk0_1624320650.sql
on TARGET system in order to create a custom SQL Profile
with plan 1624320650 linked to adjusted sql_text.


COE_XFR_SQL_PROFILE completed.

调用完这个脚本以后，会在系统的当前目录下，产生一个脚本，如这里为coe_xfr_sql_profile_auwza0aq10mk0_1624320650.sql

现在调用这个脚本，即可创建相应的SQL PROFILE

我们看执行过程（本执行过程不需要交互)

SQL>@coe_xfr_sql_profile_auwza0aq10mk0_1624320650.sql
SQL>REM
SQL>REM $Header: 215187.1 coe_xfr_sql_profile_auwza0aq10mk0_1624320650.sql 11.4.4.4 2013/10/31 carlos.sierra $
SQL>REM
SQL>REM Copyright (c) 2000-2012, Oracle Corporation. All rights reserved.
SQL>REM
SQL>REM AUTHOR
SQL>REM   carlos.sierra@oracle.com
SQL>REM
SQL>REM SCRIPT
SQL>REM   coe_xfr_sql_profile_auwza0aq10mk0_1624320650.sql
SQL>REM
SQL>REM DESCRIPTION
SQL>REM   This script is generated by coe_xfr_sql_profile.sql
SQL>REM   It contains the SQL*Plus commands to create a custom
SQL>REM   SQL Profile for SQL_ID auwza0aq10mk0 based on plan hash
SQL>REM   value 1624320650.
SQL>REM   The custom SQL Profile to be created by this script
SQL>REM   will affect plans for SQL commands with signature
SQL>REM   matching the one for SQL Text below.
SQL>REM   Review SQL Text and adjust accordingly.
SQL>REM
SQL>REM PARAMETERS
SQL>REM   None.
SQL>REM
SQL>REM EXAMPLE
SQL>REM   SQL> START coe_xfr_sql_profile_auwza0aq10mk0_1624320650.sql;
SQL>REM
SQL>REM NOTES
SQL>REM   1. Should be run as SYSTEM or SYSDBA.
SQL>REM   2. User must have CREATE ANY SQL PROFILE privilege.
SQL>REM   3. SOURCE and TARGET systems can be the same or similar.
SQL>REM   4. To drop this custom SQL Profile after it has been created:
SQL>REM	 EXEC DBMS_SQLTUNE.DROP_SQL_PROFILE(‘coe_auwza0aq10mk0_1624320650‘);
SQL>REM   5. Be aware that using DBMS_SQLTUNE requires a license
SQL>REM	 for the Oracle Tuning Pack.
SQL>REM   6. If you modified a SQL putting Hints in order to produce a desired
SQL>REM	 Plan, you can remove the artifical Hints from SQL Text pieces below.
SQL>REM	 By doing so you can create a custom SQL Profile for the original
SQL>REM	 SQL but with the Plan captured from the modified SQL (with Hints).
SQL>REM
SQL>WHENEVER SQLERROR EXIT SQL.SQLCODE;
SQL>REM
SQL>VAR signature NUMBER;
SQL>VAR signaturef NUMBER;
SQL>REM
SQL>DECLARE
  2  sql_txt CLOB;
  3  h	     SYS.SQLPROF_ATTR;
  4  PROCEDURE wa (p_line IN VARCHAR2) IS
  5  BEGIN
  6  DBMS_LOB.WRITEAPPEND(sql_txt, LENGTH(p_line), p_line);
  7  END wa;
  8  BEGIN
  9  DBMS_LOB.CREATETEMPORARY(sql_txt, TRUE);
 10  DBMS_LOB.OPEN(sql_txt, DBMS_LOB.LOB_READWRITE);
 11  -- SQL Text pieces below do not have to be of same length.
 12  -- So if you edit SQL Text (i.e. removing temporary Hints),
 13  -- there is no need to edit or re-align unmodified pieces.
 14  wa(q‘[select * from haha where a=‘10000‘]‘);
 15  DBMS_LOB.CLOSE(sql_txt);
 16  h := SYS.SQLPROF_ATTR(
 17  q‘[BEGIN_OUTLINE_DATA]‘,
 18  q‘[IGNORE_OPTIM_EMBEDDED_HINTS]‘,
 19  q‘[OPTIMIZER_FEATURES_ENABLE(‘11.2.0.3‘)]‘,
 20  q‘[DB_VERSION(‘11.2.0.3‘)]‘,
 21  q‘[FIRST_ROWS(10)]‘,
 22  q‘[OUTLINE_LEAF(@"SEL$1")]‘,
 23  q‘[INDEX_RS_ASC(@"SEL$1" "HAHA"@"SEL$1" ("HAHA"."A"))]‘,
 24  q‘[END_OUTLINE_DATA]‘);
 25  :signature := DBMS_SQLTUNE.SQLTEXT_TO_SIGNATURE(sql_txt);
 26  :signaturef := DBMS_SQLTUNE.SQLTEXT_TO_SIGNATURE(sql_txt, TRUE);
 27  DBMS_SQLTUNE.IMPORT_SQL_PROFILE (
 28  sql_text	 => sql_txt,
 29  profile	 => h,
 30  name	 => ‘coe_auwza0aq10mk0_1624320650‘,
 31  description => ‘coe auwza0aq10mk0 1624320650 ‘||:signature||‘ ‘||:signaturef||‘‘,
 32  category	 => ‘DEFAULT‘,
 33  validate	 => TRUE,
 34  replace	 => TRUE,
 35  force_match => FALSE /* TRUE:FORCE (match even when different literals in SQL). FALSE:EXACT (similar to CURSOR_SHARING) */ );
 36  DBMS_LOB.FREETEMPORARY(sql_txt);
 37  END;
 38  /

PL/SQL procedure successfully completed.

SQL>WHENEVER SQLERROR CONTINUE
SQL>SET ECHO OFF;

	    SIGNATURE
---------------------
  3625523284774604774


	   SIGNATUREF
---------------------
  2229953407394936365


... manual custom SQL Profile has been created


COE_XFR_SQL_PROFILE_auwza0aq10mk0_1624320650 completed

现在SQL profile已经创建好了，我们来执行对应的sql语句，并查看相应的执行计划

SQL>select * from haha where a=‘10000‘;

A					B
------------------------------ ----------
10000				    10000

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

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
SQL_ID	auwza0aq10mk0, child number 1
-------------------------------------
select * from haha where a=‘10000‘

Plan hash value: 1624320650

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

| Id  | Operation		    | Name     | Rows  | Bytes | Cost (%CPU)| Ti
me     |

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------

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

|   0 | SELECT STATEMENT	    |	       |       |       | 14685 (100)|
       |

|   1 |  TABLE ACCESS BY INDEX ROWID| HAHA     |     1 |    11 | 14685	 (1)| 00
:02:57 |

|*  2 |   INDEX RANGE SCAN	    | HAHA_IDX |     1 |       |   178	 (0)| 00

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
:00:03 |

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


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

   2 - access("A"=‘10000‘)


PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
Note
-----
   - SQL profile coe_auwza0aq10mk0_1624320650 used for this statement


23 rows selected.

注意看，INDEX RANGE SCAN，以及Note部分显示的，现在该SQL的执行计划已经稳定下来。

如果我们不想使用该SQL_PROFILE了该怎么办？

我们可以将SQLPROFILE删除（dbms_sqltune.drop_sql_profile）

命令本身很简单。

SQL>exec dbms_sqltune.drop_sql_profile(name=>‘coe_auwza0aq10mk0_1624320650‘);

PL/SQL procedure successfully completed.

现在我们看执行计划

SQL>select * from haha where a=‘10000‘;

A					B
------------------------------ ----------
10000				    10000

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

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
SQL_ID	auwza0aq10mk0, child number 1
-------------------------------------
select * from haha where a=‘10000‘

Plan hash value: 3694936490

--------------------------------------------------------------------------
| Id  | Operation	  | Name | Rows  | Bytes | Cost (%CPU)| Time	 |
--------------------------------------------------------------------------
|   0 | SELECT STATEMENT  |	 |	 |	 |    32 (100)| 	 |
|*  1 |  TABLE ACCESS FULL| HAHA |     1 |    11 |    32   (4)| 00:00:01 |

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
--------------------------------------------------------------------------

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

   1 - filter("A"=‘10000‘)


18 rows selected.

执行计划变回了 table access full。Note部分也消失不见。

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