Oracle10g新特性：使用DBMS_SQLTUNE优化SQL

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：

NING@ning>DECLARE
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

NING@ning>exec dbms_sqltune.execute_tuning_task(‘sql_tuning_test’);

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。
NING@ning>SELECT status FROM USER_ADVISOR_TASKS WHERE task_name = ‘sql_tuning_test’;

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 LONG 999999
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

NING@ning>exec dbms_sqltune.drop_tuning_task(‘sql_tuning_test’);

PL/SQL procedure successfully completed.