关于outline的一点测试和总结

我们知道 outlines 特性在oracle 8i就引入了，不过我用的很少，今天同事问到了，
我也就再回顾温习一下，如下是做的简单测试。

首先来看看2个跟outline相关的参数：

create_stored_outlines -- 控制是否自动创建outline
use_stored_outlines -- 控制是否启用outline

使用outline的方式有很多种，列出如下几种方式：

1. 针对sql语句或sqlid

SQL> conn roger/roger
Connected.

SQL> alter session set create_stored_outlines = true;

Session altered.

SQL> select * from v$version where rownum <2;

BANNER
----------------------------------------------------------------
Oracle Database 10g Enterprise Edition Release 10.2.0.4.0 - Prod

SQL> CREATE OUTLINE test_id FOR CATEGORY test_outlines ON
  2  SELECT owner,object_id
  3  FROM test_ht
  4  WHERE object_id=:p;

Outline created.

SQL> select name,category,sql_text from user_outlines where category=upper('test_outlines');

NAME      CATEGORY          SQL_TEXT                                              
--------- ----------------- -------------------------------------------------------
TEST_ID   TEST_OUTLINES     select owner,object_id from test_ht where object_id=:p

SQL> select * from user_outline_hints where name=upper('test_id');

NAME    NODE  STAGE JOIN_POS HINT                                                           
------- ---- ------ -------- ----------------------------------------------------------------
TEST_ID    1      1        1 INDEX_RS_ASC(@"SEL$1" "TEST_HT"@"SEL$1" ("TEST_HT"."OBJECT_ID"))
TEST_ID    1      1        0 OUTLINE_LEAF(@"SEL$1")
TEST_ID    1      1        0 ALL_ROWS
TEST_ID    1      1        0 OPTIMIZER_FEATURES_ENABLE('10.2.0.4')
TEST_ID    1      1        0 IGNORE_OPTIM_EMBEDDED_HINTS

SQL> select name,category,used from user_outlines where category=upper('test_outlines');

NAME            CATEGORY                       USED
--------------- ------------------------------ ------
TEST_ID         TEST_OUTLINES                  UNUSED

-- 该outline未使用

SQL> var p number;
SQL> exec :p :=1000;

PL/SQL procedure successfully completed.

SQL> select name,category,used from user_outlines where category=upper('test_outlines');

NAME            CATEGORY                       USED
--------------- ------------------------------ ------
TEST_ID         TEST_OUTLINES                  UNUSED

SQL>

-- 设置参数use_stored_outlines

SQL> var p number;
SQL> exec :p :=10000;

PL/SQL procedure successfully completed.

SQL> select owner,object_id from test_ht where object_id=:p;

OWNER                           OBJECT_ID
------------------------------ ----------
WMSYS                               10000

SQL>  select name,category,used from user_outlines where category=upper('test_outlines');

NAME            CATEGORY                       USED
--------------- ------------------------------ ------
TEST_ID         TEST_OUTLINES                  UNUSED

SQL> alter session set use_stored_outlines=TEST_OUTLINES;

Session altered.

SQL>  var p number;
SQL> exec :p :=20000;

PL/SQL procedure successfully completed.

SQL> select owner,object_id from test_ht where object_id=:p;

OWNER                           OBJECT_ID
------------------------------ ----------
SYS                                 20000

SQL> select name,category,used from user_outlines where category=upper('test_outlines');

NAME            CATEGORY                       USED
--------------- ------------------------------ ------
TEST_ID         TEST_OUTLINES                  USED

SQL> select sql_id,sql_text from v$sqlarea where sql_text like '{39ecd679003247f2ed728ad9c7ed019a369dd84d0731b449c26bf628d3c1a20b}select owner,object_id{39ecd679003247f2ed728ad9c7ed019a369dd84d0731b449c26bf628d3c1a20b}';

SQL_ID        SQL_TEXT
------------- ---------------------------------------------------------------------------
3v6z2kwca0ttm select sql_id,sql_text from v$sqlarea where sql_text like '{39ecd679003247f2ed728ad9c7ed019a369dd84d0731b449c26bf628d3c1a20b}select owner,ob
              ject_id{39ecd679003247f2ed728ad9c7ed019a369dd84d0731b449c26bf628d3c1a20b}'

45s1gxyr1y5k3 select owner,object_id from test_ht where object_id=:p
6cc34dzmkg686 create table test_ht as select owner,object_id,object_name from dba_objects

SQL> select * from table(dbms_xplan.DISPLAY_CURSOR('&sql_id',null));

Enter value for sql_id: 45s1gxyr1y5k3
old   1: select * from table(dbms_xplan.DISPLAY_CURSOR('&sql_id',null))
new   1: select * from table(dbms_xplan.DISPLAY_CURSOR('45s1gxyr1y5k3',null))

PLAN_TABLE_OUTPUT
-----------------------------------------------------------------------------------------------
SQL_ID  45s1gxyr1y5k3, child number 0
-------------------------------------
select owner,object_id from test_ht where object_id=:p

Plan hash value: 793292976

---------------------------------------------------------------------------------------
| Id  | Operation                   | Name    | Rows  | Bytes | Cost ({39ecd679003247f2ed728ad9c7ed019a369dd84d0731b449c26bf628d3c1a20b}CPU)| Time     |
---------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT            |         |       |       |     2 (100)|          |
|   1 |  TABLE ACCESS BY INDEX ROWID| TEST_HT |     1 |     9 |     2   (0)| 00:00:01 |

PLAN_TABLE_OUTPUT
-----------------------------------------------------------------------------------------------
|*  2 |   INDEX RANGE SCAN          | IDX_ID  |     1 |       |     1   (0)| 00:00:01 |
---------------------------------------------------------------------------------------

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

   2 - access("OBJECT_ID"=:P)

SQL_ID  45s1gxyr1y5k3, child number 1
-------------------------------------
select owner,object_id from test_ht where object_id=:p

PLAN_TABLE_OUTPUT
-----------------------------------------------------------------------------------------------

Plan hash value: 793292976

---------------------------------------------------------------------------------------
| Id  | Operation                   | Name    | Rows  | Bytes | Cost ({39ecd679003247f2ed728ad9c7ed019a369dd84d0731b449c26bf628d3c1a20b}CPU)| Time     |
---------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT            |         |       |       |     2 (100)|          |
|   1 |  TABLE ACCESS BY INDEX ROWID| TEST_HT |     1 |     9 |     2   (0)| 00:00:01 |
|*  2 |   INDEX RANGE SCAN          | IDX_ID  |     1 |       |     1   (0)| 00:00:01 |
---------------------------------------------------------------------------------------

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

   2 - access("OBJECT_ID"=:P)

Note
-----
   - outline "TEST_ID" used for this statement

42 rows selected.

-- 对于存在的cursor创建outline

SQL> select owner,object_id,object_name from test_ht where object_id=3000;

OWNER           OBJECT_ID  OBJECT_NAME
-------------- ----------  --------------------------
SYS                  3000  EXU8SYNU


SQL> select sql_id,sql_text from v$sqlarea where sql_text like '{39ecd679003247f2ed728ad9c7ed019a369dd84d0731b449c26bf628d3c1a20b}select owner,object_id{39ecd679003247f2ed728ad9c7ed019a369dd84d0731b449c26bf628d3c1a20b}';

SQL_ID        SQL_TEXT
------------- ---------------------------------------------------------------------------
3v6z2kwca0ttm select sql_id,sql_text from v$sqlarea where sql_text like '{39ecd679003247f2ed728ad9c7ed019a369dd84d0731b449c26bf628d3c1a20b}select owner,ob
              ject_id{39ecd679003247f2ed728ad9c7ed019a369dd84d0731b449c26bf628d3c1a20b}'

8gz444rhg594f select owner,object_id,object_name from test_ht where object_id=3000

SQL> select hash_value, child_number, sql_text from v$sql where sql_text like '{39ecd679003247f2ed728ad9c7ed019a369dd84d0731b449c26bf628d3c1a20b}select owner,object_id{39ecd679003247f2ed728ad9c7ed019a369dd84d0731b449c26bf628d3c1a20b}';

HASH_VALUE CHILD_NUMBER SQL_TEXT
---------- ------------ ---------------------------------------------------------------------------
 413165363            0 select sql_id,sql_text from v$sqlarea where sql_text like '{39ecd679003247f2ed728ad9c7ed019a369dd84d0731b449c26bf628d3c1a20b}select owner,ob
                        ject_id{39ecd679003247f2ed728ad9c7ed019a369dd84d0731b449c26bf628d3c1a20b}'

  47485093            0 select hash_value, child_number, sql_text from v$sql where sql_text like '{39ecd679003247f2ed728ad9c7ed019a369dd84d0731b449c26bf628d3c1a20b}
                        select owner,object_id{39ecd679003247f2ed728ad9c7ed019a369dd84d0731b449c26bf628d3c1a20b}'

3773998222            0 select owner,object_id,object_name from test_ht where object_id=3000

SQL> exec dbms_outln.create_outline(3773998222,0);

PL/SQL procedure successfully completed.

SQL> select owner,object_id,object_name from test_ht where object_id=3000;

OWNER                           OBJECT_ID OBJECT_NAME
------------------------------ ---------- --------------------
SYS                                  3000 EXU8SYNU

SQL> select hash_value, child_number, sql_text 
  2  from v$sql 
  3  where sql_text like '{39ecd679003247f2ed728ad9c7ed019a369dd84d0731b449c26bf628d3c1a20b}select owner,object_id{39ecd679003247f2ed728ad9c7ed019a369dd84d0731b449c26bf628d3c1a20b}';

HASH_VALUE CHILD_NUMBER SQL_TEXT
---------- ------------ ---------------------------------------------------------------------------
 413165363            0 select sql_id,sql_text from v$sqlarea where sql_text like '{39ecd679003247f2ed728ad9c7ed019a369dd84d0731b449c26bf628d3c1a20b}select owner,ob
                        ject_id{39ecd679003247f2ed728ad9c7ed019a369dd84d0731b449c26bf628d3c1a20b}'

  47485093            0 select hash_value, child_number, sql_text from v$sql where sql_text like '{39ecd679003247f2ed728ad9c7ed019a369dd84d0731b449c26bf628d3c1a20b}
                        select owner,object_id{39ecd679003247f2ed728ad9c7ed019a369dd84d0731b449c26bf628d3c1a20b}'

3773998222            0 select owner,object_id,object_name from test_ht where object_id=3000

SQL> select * from table(dbms_xplan.display_cursor('8gz444rhg594f'));

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------------------------
SQL_ID  8gz444rhg594f, child number 0
-------------------------------------
select owner,object_id,object_name from test_ht where object_id=3000

Plan hash value: 793292976

---------------------------------------------------------------------------------------
| Id  | Operation                   | Name    | Rows  | Bytes | Cost ({39ecd679003247f2ed728ad9c7ed019a369dd84d0731b449c26bf628d3c1a20b}CPU)| Time     |
---------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT            |         |       |       |     2 (100)|          |
|   1 |  TABLE ACCESS BY INDEX ROWID| TEST_HT |     1 |    33 |     2   (0)| 00:00:01 |

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------------------------
|*  2 |   INDEX RANGE SCAN          | IDX_ID  |     1 |       |     1   (0)| 00:00:01 |
---------------------------------------------------------------------------------------

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

   2 - access("OBJECT_ID"=3000)

Note
-----
   - outline "SYS_OUTLINE_11071210544304523" used for this statement

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------------------------

23 rows selected.

SQL> select name,CATEGORY,USED,SQL_TEXT from user_outlines
  2  where name='SYS_OUTLINE_11071210544304523';

NAME                            CATEGORY    USED   SQL_TEXT
------------------------------- ----------- ------ ---------------------------------------------------------------------------
SYS_OUTLINE_11071210544304523   DEFAULT     USED   select owner,object_id,object_name from test_ht where object_id=3000

这里需要说明一下的是alter session set create_stored_outlines = true;这是由于bug5454975的缘故（10204已经修复）
虽然我这里是10204，不过我还是设置了一下，列出来说明，以提醒大家。详见metalink ID 445126.1

最后再补充一下，如果不用outline，那么可以将其删除，可以通过如下的几种方式：

execute DBMS_OUTLN.drop_by_cat('TEST_OUTLINES');

execute DBMS_OUTLN.CLEAR_USED('TEST_OUTLINES');

execute DBMS_OUTLN.drop_unused; -- 这是删除所有状态为unused的outline，要慎重。

SQL> show parameter outline

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
_outline_bitmap_tree                 boolean     TRUE
_plan_outline_data                   boolean     TRUE
create_stored_outlines               string

关于outlines的使用，有几个需要注意的地方：


1. 参数cursor_sharing设置为force时，outlines将无效；
2. literial sql的共享程度不高的情况下，使用outline会生产很多个执行计划，可能会有一些问题；
3. 一般情况我们在使用outline的时候，也是发现某个sql的执行计划不稳定的时候，由于执行计划是基于
统计信息的，那么由于生产系统中统计信息可能是在不断的变化，那么使用outline固定的执行计划不见得
一定就是最好的，这一点需要考虑。
4. 由于outlines信息的存放在用户outln下，那么该用户就显得尤为重要，维护的时候需要注意，不能随便给drop了。
5. outline创建以后，不是说就一层不变了，可以进行编辑，至于什么时候编辑，怎么编辑，大家可以参考
metalink文档 730062.1 How to Edit a Stored Outline to Use the Plan from Another Stored Outline。