初次使用SQL调优建议工具--SQL Tuning Advisor

   在10g中，Oracle推出了自己的SQL优化辅助工具: SQL优化器(SQL Tuning Advisor ：STA)，它是新的DBMS_SQLTUNE包。使用STA一定要保证优化器是CBO模式下。但是我认为使用这种工具，仅适合完全不懂SQL的调优的人群，不要认为工具能解决好问题。SQL说到底是表达的是一个业务，工具怎么可能理解业务。SQL调优还是要用autotrace,10046,10053,display_cursor这些优秀的工具做诊断，然后根据业务和所具备的oracle基础的知识进行调优，这是最好的方法。今天在这里玩这个工具只是玩票。

1.创建数据，故意不建索引，然后做查询

SQL> create table test1 as select * from dba_objects;
SQL> create table test2 as select * from dba_objects;
SQL> exec dbms_stats.gather_table_stats(user,'test1');
SQL> exec dbms_stats.gather_table_stats(user,'test2');
SQL> set timing on
SQL> set autotrace traceonly
SQL> select count(*) from test1 t1, test2 t2 where t1.object_id = t2.object_id;
已用时间:  00: 00: 00.07
执行计划
----------------------------------------------------------
Plan hash value: 2544416891
-----------------------------------------------------------------------------
| Id  | Operation           | Name  | Rows  | Bytes | Cost (%CPU)| Time     |
-----------------------------------------------------------------------------
|   0 | SELECT STATEMENT    |       |     1 |    10 |   298   (1)| 00:00:04 |
|   1 |  SORT AGGREGATE     |       |     1 |    10 |            |          |
|*  2 |   HASH JOIN         |       | 50981 |   497K|   298   (1)| 00:00:04 |
|   3 |    TABLE ACCESS FULL| TEST1 | 50982 |   248K|   149   (1)| 00:00:02 |
|   4 |    TABLE ACCESS FULL| TEST2 | 50983 |   248K|   149   (1)| 00:00:02 |
-----------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
   2 - access("T1"."OBJECT_ID"="T2"."OBJECT_ID")
统计信息
----------------------------------------------------------
          1  recursive calls
          0  db block gets
       1410  consistent gets
          0  physical reads
          0  redo size
        410  bytes sent via SQL*Net to client
        385  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          1  rows processed
SQL> set autotrace off


2.通过DBMS_SQLTUNE包的CREATE_TUNING_TASK来创建一个优化任务，然后通过DBMS_SQLTUNE.EXECUTE_TUNING_TASK来执行调优任务，生成调优建议。
SQL> DECLARE
       my_task_name VARCHAR2(300);
       my_sqltext   CLOB;
     BEGIN
       my_sqltext := 'select count(*) from test1 t1, test2 t2 where t1.object_id = t2.object_id';
       my_task_name := DBMS_SQLTUNE.CREATE_TUNING_TASK(
               sql_text    => my_sqltext,
               user_name   => 'TEST',   -- 必须大写
               scope       => 'COMPREHENSIVE',
               time_limit  => 10,
               task_name   => 'tuning_sql_test',
               description => 'Task to tune a query on a specified table');
       DBMS_SQLTUNE.EXECUTE_TUNING_TASK( task_name => 'tuning_sql_test');
     END;
/

官方文档解析：
sql_text     The text of a SQL statement
user_name    The username for whom the statement is to be tuned
scope        Tuning scope (limited/comprehensive)
time_limit   The maximum duration in seconds for the tuning session
task_name    An optional tuning task name
description  A task of the SQL tuning session to a maximum of 256 characters
          
3.检查优化任务的状态          
SQL> select task_name,ADVISOR_NAME,STATUS from  user_advisor_tasks;
TASK_NAME                      ADVISOR_NAME                   STATUS
------------------------------ ------------------------------ -----------
tuning_sql_test                SQL Tuning Advisor             COMPLETED

4.查看优化结果
SQL> set LONGCHUNKSIZE 999999
SQL> set serveroutput on size 999999
SQL> set long 999999
SQL> select dbms_sqltune.report_tuning_task('tuning_sql_test') from dual;
DBMS_SQLTUNE.REPORT_TUNING_TASK('TUNING_SQL_TEST')
------------------------------------------------------------------------------------------------
GENERAL INFORMATION SECTION
-------------------------------------------------------------------------------
Tuning Task Name                  : tuning_sql_test
Tuning Task Owner                 : TEST
Scope                             : COMPREHENSIVE
Time Limit(seconds)               : 10
Completion Status                 : COMPLETED
Started at                        : 05/23/2014 08:50:40
Completed at                      : 05/23/2014 08:50:41
Number of Index Findings          : 1
-------------------------------------------------------------------------------
Schema Name: TEST
SQL ID     : afjq3us3nf5dt
SQL Text   : select count(*) from test1 t1, test2 t2 where t1.object_id =
             t2.object_id
-------------------------------------------------------------------------------
FINDINGS SECTION (1 finding)
-------------------------------------------------------------------------------
1- Index Finding (see explain plans section below)
--------------------------------------------------
通过创建一个或多个索引可以
  Recommendation (estimated benefit: 100%)
  ----------------------------------------
  -考虑运行可以改进物理方案设计的 Access Advi
    create index TEST.IDX$$_0C890001 on TEST.TEST1('OBJECT_ID');

  -考虑运行可以改进物理方案设计的 Access Advi
    create index TEST.IDX$$_0C890002 on TEST.TEST2('OBJECT_ID');

  Rationale
  ---------
创建推荐的索引可以显著地改进此语句的执行计划。但是, 使用典型的
 可能比单个语句更可取。通过这种方法可以获得全面的索引建
-------------------------------------------------------------------------------
EXPLAIN PLANS SECTION
-------------------------------------------------------------------------------
1- Original
-----------
Plan hash value: 2544416891
-----------------------------------------------------------------------------
| Id  | Operation           | Name  | Rows  | Bytes | Cost (%CPU)| Time     |
-----------------------------------------------------------------------------
|   0 | SELECT STATEMENT    |       |     1 |    10 |   298   (1)| 00:00:04 |
|   1 |  SORT AGGREGATE     |       |     1 |    10 |            |          |
|*  2 |   HASH JOIN         |       | 50981 |   497K|   298   (1)| 00:00:04 |
|   3 |    TABLE ACCESS FULL| TEST1 | 50982 |   248K|   149   (1)| 00:00:02 |
|   4 |    TABLE ACCESS FULL| TEST2 | 50983 |   248K|   149   (1)| 00:00:02 |
-----------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
   2 - access("T1"."OBJECT_ID"="T2"."OBJECT_ID")

2- Using New Indices
--------------------
Plan hash value: 3060659111
-----------------------------------------------------------------------------------------
| Id  | Operation              | Name           | Rows  | Bytes | Cost (%CPU)| Time     |
-----------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT       |                |     1 |    10 |    53   (2)| 00:00:01 |
|   1 |  SORT AGGREGATE        |                |     1 |    10 |            |          |
|*  2 |   HASH JOIN            |                | 50981 |   497K|    53   (2)| 00:00:01 |
|   3 |    INDEX FAST FULL SCAN| IDX$$_0C890001 | 50982 |   248K|    26   (0)| 00:00:01 |
|   4 |    INDEX FAST FULL SCAN| IDX$$_0C890002 | 50983 |   248K|    26   (0)| 00:00:01 |
-----------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
   2 - access("T1"."OBJECT_ID"="T2"."OBJECT_ID")
-------------------------------------------------------------------------------

5.验证一下

 根据advisor的建议进行调优，1410降到204，是乎有点效果。

SQL>create index ind_t1_object_id  on test1(object_id);

SQL> create index ind_t2_object_id  on test2(object_id);

SQL> set autotrace traceonly
SQL> select count(*) from test1 t1, test2 t2 where t1.object_id = t2.object_id;
已用时间:  00: 00: 00.06
执行计划
----------------------------------------------------------
Plan hash value: 1069114244
-------------------------------------------------------------------------------------------
| Id  | Operation              | Name             | Rows  | Bytes | Cost (%CPU)| Time     |
-------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT       |                  |     1 |    10 |    51   (2)| 00:00:01 |
|   1 |  SORT AGGREGATE        |                  |     1 |    10 |            |          |
|*  2 |   HASH JOIN            |                  | 50981 |   497K|    51   (2)| 00:00:01 |
|   3 |    INDEX FAST FULL SCAN| IND_T1_OBJECT_ID | 50982 |   248K|    25   (0)| 00:00:01 |
|   4 |    INDEX FAST FULL SCAN| IND_T2_OBJECT_ID | 50983 |   248K|    25   (0)| 00:00:01 |
-------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
   2 - access("T1"."OBJECT_ID"="T2"."OBJECT_ID")
统计信息
----------------------------------------------------------
          1  recursive calls
          0  db block gets
        240  consistent gets
        226  physical reads
          0  redo size
        410  bytes sent via SQL*Net to client
        385  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          1  rows processed

6.删除优化任务
SQL> exec dbms_sqltune.drop_tuning_task('tuning_sql_test');