关于outline的一点测试和总结-CFANZ编程社区

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。
首先先来看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：

针对sql语句或sqlid

1. 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>
SQL> create outline test_id for CATEGORY test_outlines on 
  2  select owner,object_id from test_ht 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
 
SQL>  --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
  2  ;
 
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>
SQL> select name,category,used from user_outlines where category=upper('test_outlines');
 
NAME            CATEGORY                       USED
--------------- ------------------------------ ------
TEST_ID         TEST_OUTLINES                  USED
 
SQL>
SQL> select sql_id,sql_text from v$sqlarea where sql_text like '%select owner,object_id%';
 
SQL_ID        SQL_TEXT
------------- ---------------------------------------------------------------------------
3v6z2kwca0ttm select sql_id,sql_text from v$sqlarea where sql_text like '%select owner,ob
              ject_id%'
 
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 (%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 (%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.
 
SQL>
 
----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 '%select owner,object_id%';
 
SQL_ID        SQL_TEXT
------------- ---------------------------------------------------------------------------
3v6z2kwca0ttm select sql_id,sql_text from v$sqlarea where sql_text like '%select owner,ob
              ject_id%'
 
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 '%select owner,object_id%';
 
HASH_VALUE CHILD_NUMBER SQL_TEXT
---------- ------------ ---------------------------------------------------------------------------
 413165363            0 select sql_id,sql_text from v$sqlarea where sql_text like '%select owner,ob
                        ject_id%'
 
  47485093            0 select hash_value, child_number, sql_text from v$sql where sql_text like '%
                        select owner,object_id%'
 
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>
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 from v$sql where sql_text like '%select owner,object_id%';
 
HASH_VALUE CHILD_NUMBER SQL_TEXT
---------- ------------ ---------------------------------------------------------------------------
 413165363            0 select sql_id,sql_text from v$sqlarea where sql_text like '%select owner,ob
                        ject_id%'
 
  47485093            0 select hash_value, child_number, sql_text from v$sql where sql_text like '%
                        select owner,object_id%'
 
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 (%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
 
SQL>

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
SQL>
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。