PLSQL_性能优化工具系列07_SQL Tuning Advisor

2014-10-02 Created By BaoXinjian

一、摘要

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SQL优化是有一定难度的工作，需要DBA具有扎实的知识和较丰富的经验。

在ORACLE10g以后，引入了一些自动调优技术，包括sql tuning advisor、sql access advisor、ADDM等，不需要了解JOIN的类型、次序，也不需了解优化器，新手也能用这些工具进行一些优化工作。

 

二、SQL Tunning Advisor

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SQL Tuning Advisor可以在Enterprise Manager图形界面中调用，也可通过过程包调用。

1. 以下内容可以作为sql tuning advisor的输入，调优其中的问题sql：

• l Addm （每小时自动运行）
• l Awr
• l Shared sql area
• l Sql tuning set

2. 调用sql tuning advisor时，优化器进入调优模式。

Oracle优化器有两种模式：

(1). Normal mode

快速产生对大多数sql来说合理的计划。要求生成计划的时间非常短。

(2).Tuning mode

进行额外分析，如sql结构分析、sql profile、访问路径分析、替代写法等等，给出优化建议。通常调优一句sql需要几分钟，下面减少其中的sql profile。

 

三、SQL Profile

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SQL Profile不是执行计划，而是提供以下信息帮助优化器选择plan

1. 环境：db配置，绑定变量值，optimizer statistics,data set

2. Supplemental Statistics

因此可以说sql profile之于sql，相当于optimizer statistics之于table/index。

3.  SQL Profile的优点是：

• 与hints不同，使用sql profile不需改源程序。这点和outline一样
• 与hint和stored outline不同，profile通常不会固定执行计划，而是纠正优化器不正确的估计，因此在不同环境下更有弹性

4. Sql profile用来优化sql。当然使用了sql profile之后，也会达到稳定执行计划的目的。

 

四、案例

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案例：通过SQL Tunning Advisor查找SQL现有的效率和推荐的最优化SQL Plan

Step1. 准备权限

CONNECT / AS SYSDBA GRANT ADVISOR TO SYSTEM; GRANT SELECT_CATALOG_ROLE TO SYSTEM; GRANT EXECUTE ON DBMS_SQLTUNE TO SYSTEM;

Step2. Create Task创建诊断任务

DECLARE bxj_task_name VARCHAR2 (30); bxj_sqltext CLOB; BEGIN bxj_sqltext :=

         'SELECT * '

      || 'FROM sh.sales '

      || 'WHERE prod_id = 10 AND '

      || 'cust_id = 100 '; DBMS_OUTPUT.PUT_LINE (bxj_sqltext); bxj_task_name := DBMS_SQLTUNE.CREATE_TUNING_TASK ( sql_text => bxj_sqltext, user_name     => 'SYSTEM', scope => 'COMPREHENSIVE', time_limit => 60, task_name => 'BXJ_SQL_TUNING_TASK', description => 'Task To Tune A Query On A Specified PRODUCT' ); END;

Step3. Query  Task查询诊断任务状态

SELECT task_name FROM dba_advisor_log WHERE   task_name = 'BXJ_SQL_TUNING_TASK';

Step4. Execute Task执行诊断任务

BEGIN DBMS_SQLTUNE.EXECUTE_TUNING_TASK (task_name => 'BXJ_SQL_TUNING_TASK'); END;

Step5. Query  Task查询诊断任务状态

SELECT task_id, task_name, status FROM dba_advisor_log WHERE   task_name = 'BXJ_SQL_TUNING_TASK';

Step6. Task Result查看诊断人任务结果

SELECT   DBMS_SQLTUNE.REPORT_TUNING_TASK ('BXJ_SQL_TUNING_TASK') FROM DUAL;

 

GENERAL INFORMATION SECTION -------------------------------------------------------------------------------

Tuning Task Name : BXJ_SQL_TUNING_TASK Tuning Task Owner : SYSTEM Workload Type : Single SQL Statement Scope : COMPREHENSIVE Time Limit(seconds): 60 Completion Status : COMPLETED Started at : 10/02/2014 04:08:26 Completed at : 10/02/2014 04:08:27



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

Schema Name: SYSTEM SQL ID : 276wx1tuaxwpg SQL Text   : SELECT * FROM sh.sales WHERE prod_id = 10 AND cust_id = 100 



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

FINDINGS SECTION (2 findings) -------------------------------------------------------------------------------



1- SQL Profile Finding (see explain plans section below) --------------------------------------------------------

  A potentially better execution plan was found for this statement. Recommendation (estimated benefit: 25.02%) ------------------------------------------

  - Consider accepting the recommended SQL profile. execute dbms_sqltune.accept_sql_profile(task_name =>

            'BXJ_SQL_TUNING_TASK', task_owner => 'SYSTEM', replace => TRUE); Validation results ------------------

  The SQL profile was tested by executing both its plan and the original plan

  and measuring their respective execution statistics. A plan may have been only partially executed if the other could be run to completion in less time. Original Plan  With SQL Profile  % Improved ------------- ---------------- ----------

 Completion Status: COMPLETE COMPLETE Elapsed Time(us): 211                70      66.82 % CPU Time(us): 299               100      66.55 %

  User I/O Time(us):                  0                 0 Buffer Gets: 52                39         25 % Physical Read Requests:             0                 0 Physical Write Requests: 0                 0 Physical Read Bytes:                0                 0 Physical Write Bytes: 0                 0 Rows Processed: 0                 0 Fetches: 0                 0 Executions: 1                 1 Notes -----

  1. The original plan was first executed to warm the buffer cache. 2. Statistics for original plan were averaged over next 9 executions. 3. The SQL profile plan was first executed to warm the buffer cache. 4. Statistics for the SQL profile plan were averaged over next 9 executions. 2- Index Finding (see explain plans section below) --------------------------------------------------

  The execution plan of this statement can be improved by creating one or more indices. Recommendation (estimated benefit: 86.25%) ------------------------------------------

  - Consider running the Access Advisor to improve the physical schema design or creating the recommended index.  If you choose to create the recommended index, consider dropping the index "SH"."SALES_CUST_BIX" because it is a prefix of the recommended index. create index SH.IDX$$_00270001 on SH.SALES("CUST_ID","PROD_ID"); Rationale ---------

    Creating the recommended indices significantly improves the execution plan

    of this statement. However, it might be preferable to run "Access Advisor" using a representative SQL workload as opposed to a single statement. This will allow to get comprehensive index recommendations which takes into account index maintenance overhead and additional space consumption. -------------------------------------------------------------------------------

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



1- Original With Adjusted Cost ------------------------------

Plan hash value: 811666046



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

| Id  | Operation                          | Name           | Rows  | Bytes | Cost (%CPU)| Time     | Pstart| Pstop |

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

|   0 | SELECT STATEMENT                   |                |     1 |    29 |    58   (0)| 00:00:01 |       |       |

|   1 |  PARTITION RANGE ALL               |                |     1 |    29 |    58   (0)| 00:00:01 |     1 |    28 |

|   2 |   TABLE ACCESS BY LOCAL INDEX ROWID| SALES          |     1 |    29 |    58   (0)| 00:00:01 |     1 |    28 |

|   3 |    BITMAP CONVERSION TO ROWIDS     |                |       |       |            |          |       |       |

|   4 |     BITMAP AND                     |                |       |       |            |          |       |       |

|*  5 |      BITMAP INDEX SINGLE VALUE     | SALES_CUST_BIX |       |       |            |          |     1 |    28 |

|*  6 |      BITMAP INDEX SINGLE VALUE     | SALES_PROD_BIX |       |       |            |          |     1 |    28 |

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

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

 

   5 - access("CUST_ID"=100) 6 - access("PROD_ID"=10) 2- Using SQL Profile --------------------

Plan hash value: 511273406



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

| Id  | Operation                          | Name           | Rows  | Bytes | Cost (%CPU)| Time     | Pstart| Pstop |

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

|   0 | SELECT STATEMENT                   |                |     1 |    29 |    29   (0)| 00:00:01 |       |       |

|   1 |  PARTITION RANGE ALL               |                |     1 |    29 |    29   (0)| 00:00:01 |     1 |    28 |

|*  2 |   TABLE ACCESS BY LOCAL INDEX ROWID| SALES          |     1 |    29 |    29   (0)| 00:00:01 |     1 |    28 |

|   3 |    BITMAP CONVERSION TO ROWIDS     |                |       |       |            |          |       |       |

|*  4 |     BITMAP INDEX SINGLE VALUE      | SALES_PROD_BIX |       |       |            |          |     1 |    28 |

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

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

 

   2 - filter("CUST_ID"=100) 4 - access("PROD_ID"=10) 3- Using New Indices --------------------

Plan hash value: 2089281862



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

| Id  | Operation                          | Name           | Rows  | Bytes | Cost (%CPU)| Time     | Pstart| Pstop |

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

|   0 | SELECT STATEMENT                   |                |     1 |    29 |     4   (0)| 00:00:01 |       |       |

|   1 |  TABLE ACCESS BY GLOBAL INDEX ROWID| SALES          |     1 |    29 |     4   (0)| 00:00:01 | ROWID | ROWID |

|*  2 |   INDEX RANGE SCAN                 | IDX$$_00270001 |     1 |       |     3   (0)| 00:00:01 |       |       |

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

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

 

   2 - access("CUST_ID"=100 AND "PROD_ID"=10) -------------------------------------------------------------------------------

Step7. Task Accept接受诊断任务结果

DECLARE bxj_sqlprofile_name VARCHAR2 (30); BEGIN bxj_sqlprofile_name := DBMS_SQLTUNE.ACCEPT_SQL_PROFILE (task_name   => 'BXJ_SQL_TUNING_TASK', name => 'BXJ_SQL_PROFILE'); DBMS_OUTPUT.PUT_LINE ('bxj_sqlprofile_name=' || bxj_sqlprofile_name); END;

Step8. Task Remove移除诊断任务

BEGIN DBMS_SQLTUNE.DROP_TUNING_TASK ('BXJ_SQL_TUNING_TASK'); END;

Step9. 其他信息

注意：无法使用SQL中Hints，导致Hints无法使用

SELECT * FROM DBA_SQLTUNE_STATISTICS; SELECT * FROM DBA_SQLTUNE_BINDS; SELECT * FROM DBA_SQLTUNE_PLANS;

 

Thanks and Regards

参考：metalink资料 Using the DBMS_SQLTUNE package to Run the Sql Tuning Advisor (Doc ID 262687.1)

参考：luw http://blog.itpub.net/18474/abstract/1/