SQL Tuning Advisor简单使用

SQL Tuning Advision是Oracle提供的一个功能包，可以针对有性能问题的SQL给出优化建议。可以作为调优的辅助手段。

建立测试表和索引
create table t_1 as select * from dba_objects;
create table t_2 as select * from dba_tables;
create index idx_t_2_ts on t_2(tablespace_name);

begin
  dbms_stats.gather_table_stats(ownname => user,tabname => 'T_1',cascade => true);
  dbms_stats.gather_table_stats(ownname => user,tabname => 'T_2',cascade => true);
end;
/

假设的SQL。 这些语句运行很慢，需要优化
-- stmt 1
select t2.*
  from t_1 t1, t_2 t2
 where t1.owner = t2.owner
   and t1.object_name = t2.table_name
   and t2.blocks > 10
   and t2.tablespace_name = 'USERS';

-- stmt 2
select t1.* from t_1 t1 where t1.object_type = 'TABLE';

使用SQL Tuning Advisor，察看系统提供的优化方案

Single SQL Statement

当仅仅需要察看单条语句的时候，可以直接把SQL作为参数创建一个Task

-- drop a sql tuning task
begin
  dbms_sqltune.drop_tuning_task(task_name => 'my_sql_tuning_task');
end;
/
 
-- create a sql tuning task
declare
  l_task_name varchar2(30);
  l_sqltext   clob;
begin
  l_sqltext   := --
      'select t2.*
        from t_1 t1, t_2 t2
       where t1.owner = t2.owner
         and t1.object_name = t2.table_name
         and t2.blocks > :p1
         and t2.tablespace_name = :p2';
  l_task_name := dbms_sqltune.create_tuning_task --
                 (sql_text   => l_sqltext,
                  bind_list  => sql_binds(anydata.ConvertNumber(10),
                                          anydata.ConvertVarchar2('USERS')),
                  user_name  => user,
                  scope      => dbms_sqltune.SCOPE_COMPREHENSIVE,
                  time_limit => 60,
                  task_name  => 'my_sql_tuning_task');
end;
/

select l.task_name,l.status from dba_advisor_log l where l.owner = user;

-- execute a sql tuning task
begin
  dbms_sqltune.execute_tuning_task(task_name => 'my_sql_tuning_task');
end;
/

-- check the running progress
select p.sofar, p.totalwork
  from v$advisor_progress p, dba_advisor_log l
 where p.task_id = l.task_id
   and l.task_name = 'my_sql_tuning_task';

-- display the result
set long 1000000
set linesize 100
select dbms_sqltune.report_tuning_task('my_sql_tuning_task') from dual;

节选部分结果
-------------------------------------------------------------------------------
FINDINGS SECTION (1 finding)
-------------------------------------------------------------------------------
 
1- 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: 100%)
  ----------------------------------------
  - Consider running the Access Advisor to improve the physical schema design
    or creating the recommended index.
    create index T2_1_12_6_A.IDX$$_7DCA0001 on
    T2_1_12_6_A.T_2('TABLESPACE_NAME','BLOCKS');
 
  - Consider running the Access Advisor to improve the physical schema design
    or creating the recommended index.
    create index T2_1_12_6_A.IDX$$_7DCA0002 on
    T2_1_12_6_A.T_1('OWNER','OBJECT_NAME');
 
  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
-----------
Plan hash value: 3244836478
 
--------------------------------------------------------------------------------
| Id  | Operation                    | Name       | Rows  | Bytes | Cost (%CPU)|
--------------------------------------------------------------------------------
|   0 | SELECT STATEMENT             |            |     1 |   250 |   364   (2)|
|*  1 |  HASH JOIN                   |            |     1 |   250 |   364   (2)|
|*  2 |   TABLE ACCESS BY INDEX ROWID| T_2        |     1 |   216 |     3   (0)|
|*  3 |    INDEX RANGE SCAN          | IDX_T_2_TS |    43 |       |     1   (0)|
|   4 |   TABLE ACCESS FULL          | T_1        |   148K|  4946K|   360   (1)|
--------------------------------------------------------------------------------
 
Predicate Information (identified by operation id):
---------------------------------------------------
 
   1 - access("T1"."OWNER"="T2"."OWNER" AND "T1"."OBJECT_NAME"="T2"."TABLE_NAME"
   2 - filter("T2"."BLOCKS">:P1)
   3 - access("T2"."TABLESPACE_NAME"=:P2)
 
2- Using New Indices
--------------------
Plan hash value: 1060650565
 
--------------------------------------------------------------------------------
| Id  | Operation                    | Name           | Rows  | Bytes | Cost (%C
--------------------------------------------------------------------------------
|   0 | SELECT STATEMENT             |                |     1 |   250 |     3
|   1 |  NESTED LOOPS                |                |     1 |   250 |     3
|   2 |   TABLE ACCESS BY INDEX ROWID| T_2            |     1 |   216 |     2
|*  3 |    INDEX RANGE SCAN          | IDX$$_7DCA0001 |     1 |       |     1
|*  4 |   INDEX RANGE SCAN           | IDX$$_7DCA0002 |     1 |    34 |     1
--------------------------------------------------------------------------------
 
Predicate Information (identified by operation id):
---------------------------------------------------
 
   3 - access("T2"."TABLESPACE_NAME"=:P2 AND "T2"."BLOCKS">:P1 AND "T2"."BLOCKS"
              NOT NULL)
   4 - access("T1"."OWNER"="T2"."OWNER" AND "T1"."OBJECT_NAME"="T2"."TABLE_NAME"
 
-------------------------------------------------------------------------------

SQL Tuning Set
当需要对多条语句进行察看的时候，可以使用STS。


STS可以从多种数据源(CursorCache, AWR, STS)获取SQL，这里我们从Cache中取得我们关心的几条。
SQL> select sql_id, sql_text from v$sql where lower(sql_text) like 'select t_.*%';
 
SQL_ID        SQL_TEXT
------------- --------------------------------------------------------------------------------
7rucbfq8vcr7d select t1.*   from t_1 t1    where t1.object_type = 'TABLE'
588rxmp05xt7g select t2.*   from t_1 t1, t_2 t2  where t1.owner = t2.owner    and t1.object_na

STS中实际包含的是一些sys.sqlset_row对象，他的属性可以作为筛选的条件
SQL> desc dbms_sqltune.select_cursor_cache
Parameter         Type       Mode Default?
----------------- ---------- ---- --------
(RESULT)          SYS.SQLSET              
BASIC_FILTER      VARCHAR2   IN   Y       
OBJECT_FILTER     VARCHAR2   IN   Y       
RANKING_MEASURE1  VARCHAR2   IN   Y       
RANKING_MEASURE2  VARCHAR2   IN   Y       
RANKING_MEASURE3  VARCHAR2   IN   Y       
RESULT_PERCENTAGE NUMBER     IN   Y       
RESULT_LIMIT      NUMBER     IN   Y       
ATTRIBUTE_LIST    VARCHAR2   IN   Y       
-- preview the STS contents
select t.*
  from table(dbms_sqltune.select_cursor_cache('sql_id in (''588rxmp05xt7g'',''7rucbfq8vcr7d'')')) t;

找到我们关心的sql_id之后，用这个条件构造STS

-- create a STS
begin
  dbms_sqltune.create_sqlset(sqlset_name => 'my_sts');
end;
/

-- load STS using cursor cache
declare
  l_cur dbms_sqltune.sqlset_cursor;
begin
  open l_cur for
    select value(t)
      from table(dbms_sqltune.select_cursor_cache('sql_id in (''588rxmp05xt7g'',''7rucbfq8vcr7d'')')) t;

  dbms_sqltune.load_sqlset(sqlset_name => 'my_sts', populate_cursor => l_cur);
end;
/

-- display contents of STS
select * from table(dbms_sqltune.select_sqlset('my_sts'));

-- drop a sql tuning task
begin
  dbms_sqltune.drop_tuning_task(task_name => 'my_sql_tuning_task');
end;
/
 
-- create a sql tuning task by using STS
declare
  l_task_name varchar2(30);
  l_sqltext   clob;
begin
  l_task_name := dbms_sqltune.create_tuning_task --
                 (sqlset_name => 'my_sts',
                  scope      => dbms_sqltune.SCOPE_COMPREHENSIVE,
                  time_limit => 60,
                  task_name  => 'my_sql_tuning_task');
end;
/

继续后面的执行和察看步骤（略）