在Oracle10g之前，优化SQL是个比较费力的技术活，不停的分析执行计划，加hint，分析统计信息等等，当然也有SQL调优辅助工具可以使用，只是要么价格昂贵，要么效果不佳。在10g中，Oracle推出了自己的SQL优化辅助工具，这就是新的DBMS_SQLTUNE包。执行DBMS_SQLTUNE包进行sql优化需要有advisor的权限：
SYS@ning>grant advisor to ning;
Grant succeeded.
使用DBMS_SQLTUNE包进行SQL优化，大致可以分为四个步骤：
- 创建优化任务
- 执行优化任务
- 显示优化任务的结果
- 按照建议执行优化
一、创建优化任务
使用dbms_sqltune.create_tuning_task函数来创建优化任务，该参数的声明如下：
FUNCTION CREATE_TUNING_TASK RETURNS VARCHAR2
Argument Name Type In/Out Default?
SQLSET_NAME VARCHAR2 IN
BASIC_FILTER VARCHAR2 IN DEFAULT
OBJECT_FILTER VARCHAR2 IN DEFAULT
RANK1 VARCHAR2 IN DEFAULT
RANK2 VARCHAR2 IN DEFAULT
RANK3 VARCHAR2 IN DEFAULT
RESULT_PERCENTAGE NUMBER IN DEFAULT
RESULT_LIMIT NUMBER IN DEFAULT
SCOPE VARCHAR2 IN DEFAULT
TIME_LIMIT NUMBER IN DEFAULT
TASK_NAME VARCHAR2 IN DEFAULT
DESCRIPTION VARCHAR2 IN DEFAULT
PLAN_FILTER VARCHAR2 IN DEFAULT
SQLSET_OWNER VARCHAR2 IN DEFAULT
具体每个参数的含义请参考Oracle官方文档的说明。函数的返回值为创建的任务名。下面我们创建一个叫sql_tuning_test的任务：
2 my_task_name VARCHAR2 (30);
3 my_sqltext CLOB;
4 BEGIN
5 my_sqltext := 'SELECT e.last_name, d.department_name, d.department_id
6 FROM employees e, departments d
7 WHERE e.department_id = d.department_id
8 AND d.department_id = :bnd';
9 my_task_name := dbms_sqltune.create_tuning_task (sql_text=> my_sqltext,
10 bind_list => sql_binds (anydata.convertnumber (9)),
11 user_name => 'NING',
12 scope => 'COMPREHENSIVE',
13 time_limit => 60,
14 task_name => 'sql_tuning_test',
15 description => 'Tuning Task'
16 );
17 END;
18 /
PL/SQL procedure successfully completed.
二、执行优化任务
通过调用dbms_sqltune.execute_tuning_task过程来执行前面创建好的优化任务。
PROCEDURE EXECUTE_TUNING_TASK
Argument Name Type In/Out Default?
—————– ————- —— ——–
TASK_NAME VARCHAR2 IN
PL/SQL procedure successfully completed.
三、检查优化任务的状态
通过查看user_advisor_tasks/dba_advisor_tasks视图可以查看优化任务的当前状态。
STATUS
-----------
COMPLETED
四、得到优化任务执行的结果
通过dbms_sqltune.report_tning_task函数可以获得优化任务的结果。
NING@ning>set serveroutput on size 999999
NING@ning>SET LINESIZE 100
NING@ning>SELECT DBMS_SQLTUNE.REPORT_TUNING_TASK('sql_tuning_test') FROM DUAL;
DBMS_SQLTUNE.REPORT_TUNING_TASK('SQL_TUNING_TEST')
-------------------------------------------------------------------------------
GENERAL INFORMATION SECTION
-------------------------------------------------------------------------------
Tuning Task Name : sql_tuning_test
Tuning Task Owner : NING
Scope : COMPREHENSIVE
Time Limit(seconds) : 60
Completion Status : COMPLETED
Started at : 04/30/2007 10:42:48
Completed at : 04/30/2007 10:42:49
Number of Statistic Findings : 2
Number of SQL Profile Findings : 1
DBMS_SQLTUNE.REPORT_TUNING_TASK('SQL_TUNING_TEST')
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
Schema Name: NING
SQL ID : 6rbh5v8smjpdq
SQL Text : SELECT e.last_name, d.department_name, d.department_id
FROM employees e, departments d
WHERE e.department_id = d.department_id
AND d.department_id = :bnd
-------------------------------------------------------------------------------
FINDINGS SECTION (3 findings)
DBMS_SQLTUNE.REPORT_TUNING_TASK('SQL_TUNING_TEST')
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
1- Statistics Finding
---------------------
Table "NING"."DEPARTMENTS" was not analyzed.
Recommendation
--------------
- Consider collecting optimizer statistics for this table.
execute dbms_stats.gather_table_stats(ownname => 'NING', tabname =>
'DEPARTMENTS', estimate_percent => DBMS_STATS.AUTO_SAMPLE_SIZE,
method_opt => 'FOR ALL COLUMNS SIZE AUTO');
Rationale
---------
The optimizer requires up-to-date statistics for the table in order to
select a good execution plan.
2- Statistics Finding
---------------------
Table "NING"."EMPLOYEES" was not analyzed.
Recommendation
--------------
- Consider collecting optimizer statistics for this table.
execute dbms_stats.gather_table_stats(ownname => 'NING', tabname =>
'EMPLOYEES', estimate_percent => DBMS_STATS.AUTO_SAMPLE_SIZE,
method_opt => 'FOR ALL COLUMNS SIZE AUTO');
Rationale
---------
The optimizer requires up-to-date statistics for the table in order to
select a good execution plan.
DBMS_SQLTUNE.REPORT_TUNING_TASK('SQL_TUNING_TEST')
-------------------------------------------------------------------------------
3- SQL Profile Finding (see explain plans section below)
--------------------------------------------------------
A potentially better execution plan was found for this statement.
Recommendation (estimated benefit<=10%)
---------------------------------------
- Consider accepting the recommended SQL profile.
execute dbms_sqltune.accept_sql_profile(task_name => 'sql_tuning_test',
replace => TRUE);
DBMS_SQLTUNE.REPORT_TUNING_TASK('SQL_TUNING_TEST')
------------------------------------------------------------------------------
-------------------------------------------------------------------------------
EXPLAIN PLANS SECTION
-------------------------------------------------------------------------------
1- Original With Adjusted Cost
------------------------------
Plan hash value: 2052257371
----------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
----------------------------------------------------------------------------------
DBMS_SQLTUNE.REPORT_TUNING_TASK('SQL_TUNING_TEST')
-----------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 26 | 22 (5)| 00:00:01 |
|* 1 | HASH JOIN | | 1 | 26 | 22 (5)| 00:00:01 |
|* 2 | TABLE ACCESS FULL| DEPARTMENTS | 1 | 7 | 3 (0)| 00:00:01 |
|* 3 | TABLE ACCESS FULL| EMPLOYEES | 1 | 19 | 18 (0)| 00:00:01 |
----------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - access("E"."DEPARTMENT_ID"="D"."DEPARTMENT_ID")
2 - filter("D"."DEPARTMENT_ID"=:BND)
DBMS_SQLTUNE.REPORT_TUNING_TASK('SQL_TUNING_TEST')
---------------------------------------------------------------------------------
3 - filter("E"."DEPARTMENT_ID"=:BND)
2- Using SQL Profile
--------------------
Plan hash value: 1782137809
----------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
----------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 26 | 22 (5)| 00:00:01 |
|* 1 | HASH JOIN | | 1 | 26 | 22 (5)| 00:00:01 |
DBMS_SQLTUNE.REPORT_TUNING_TASK('SQL_TUNING_TEST')
----------------------------------------------------------------------------------
|* 2 | TABLE ACCESS FULL| EMPLOYEES | 1 | 19 | 18 (0)| 00:00:01 |
|* 3 | TABLE ACCESS FULL| DEPARTMENTS | 1 | 7 | 3 (0)| 00:00:01 |
----------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - access("E"."DEPARTMENT_ID"="D"."DEPARTMENT_ID")
2 - filter("E"."DEPARTMENT_ID"=:BND)
3 - filter("D"."DEPARTMENT_ID"=:BND)
DBMS_SQLTUNE.REPORT_TUNING_TASK('SQL_TUNING_TEST')
然后我们就可以根据Recommendation部分的建议来执行优化操作了。
五、删除优化任务
通过调用dbms_sqltuen.drop_tuning_task可以删除已经存在的优化任务
PL/SQL procedure successfully completed.
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