关于oracle 10g中参数optimizer_mode的测试
今天，在资料上看到如下内容：
感到很疑惑：真的是这样么，10g中的rule和choose是无效的选项？
但我测试时，也能设置choose啊，而且执行计划和all_Rows确实不一样啊!
问了一下网上的朋友，又作了些测试如下，结果也在下面：
|
C:\Documents and Settings\Administrator>sqlplus system/manager
SQL*Plus: Release 10.2.0.1.0 - Production on 星期五 3月 19 14:06:01 2010
Copyright (c) 1982, 2005, Oracle. All rights reserved.
连接到:
Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Production
With the Partitioning, OLAP and Data Mining options
SQL> show parameter optimizer_mode
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
optimizer_mode string ALL_ROWS
SQL> alter session set optimizer_mode=rule;
会话已更改。
SQL> show parameter optimizer_mode
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
optimizer_mode string RULE
SQL> set autotrace on
SQL> select * from v$version;
BANNER
----------------------------------------------------------------
Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Prod
PL/SQL Release 10.2.0.1.0 - Production
CORE 10.2.0.1.0 Production
TNS for 32-bit Windows: Version 10.2.0.1.0 - Production
NLSRTL Version 10.2.0.1.0 - Production
执行计划
----------------------------------------------------------
Plan hash value: 1078166315
--------------------------------------
| Id | Operation | Name |
--------------------------------------
| 0 | SELECT STATEMENT | |
|* 1 | FIXED TABLE FULL| X$VERSION |
--------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter("INST_ID"=USERENV('INSTANCE'))
Note
-----
- rule based optimizer used (consider using cbo) --Oracle给出的提示
统计信息
----------------------------------------------------------
8 recursive calls
0 db block gets
2 consistent gets
0 physical reads
0 redo size
680 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)
5 rows processed
SQL> alter session set optimizer_mode=chooose;
ERROR:
ORA-00096: 值 CHOOOSE 对参数 optimizer_mode 无效, 它必须来自 first_rows_1000,
first_rows_100, first_rows_10, first_rows_1, first_rows, all_rows, choose, rule之间
-->一次错误输入，得到了参数的选项值
SQL> alter session set optimizer_mode=choose;
会话已更改。
SQL> show parameter optimizer_mode
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
optimizer_mode string CHOOSE
SQL> select * from v$version;
BANNER
----------------------------------------------------------------
Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Prod
PL/SQL Release 10.2.0.1.0 - Production
CORE 10.2.0.1.0 Production
TNS for 32-bit Windows: Version 10.2.0.1.0 - Production
NLSRTL Version 10.2.0.1.0 - Production
执行计划
----------------------------------------------------------
Plan hash value: 1078166315
--------------------------------------
| Id | Operation | Name |
--------------------------------------
| 0 | SELECT STATEMENT | |
|* 1 | FIXED TABLE FULL| X$VERSION |
--------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter("INST_ID"=USERENV('INSTANCE'))
Note
-----
- rule based optimizer used (consider using cbo) --Oracle给出的提示
统计信息
----------------------------------------------------------
8 recursive calls
0 db block gets
2 consistent gets
0 physical reads
0 redo size
680 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)
5 rows processed
SQL> alter session set optimizer_mode=all_rows;
会话已更改。
SQL> show parameter optimizer_mode
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
optimizer_mode string ALL_ROWS
SQL> select * from v$version;
BANNER
----------------------------------------------------------------
Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Prod
PL/SQL Release 10.2.0.1.0 - Production
CORE 10.2.0.1.0 Production
TNS for 32-bit Windows: Version 10.2.0.1.0 - Production
NLSRTL Version 10.2.0.1.0 - Production
执行计划
----------------------------------------------------------
Plan hash value: 1078166315
------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 47 | 0 (0)| 00:00:01 |
|* 1 | FIXED TABLE FULL| X$VERSION | 1 | 47 | 0 (0)| 00:00:01 |
------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter("INST_ID"=USERENV('INSTANCE'))
统计信息
----------------------------------------------------------
8 recursive calls
0 db block gets
2 consistent gets
0 physical reads
0 redo size
680 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)
5 rows processed
SQL>
|
测试结果：
1，并非如资料中所言，rule，choose仍然是有效选项，可以选择。
2，但rule和choose非oracle推荐值，当设置为rule或choose时，oracle会在执行计划中给出提示：- rule based optimizer used (consider using cbo)
3，oracle10g中optimizer_mode选择范围： first_rows_1000,first_rows_100,first_rows_10, first_rows_1, first_rows, all_rows, choose, rule。
4，此测试必须在oracle10g的sqlplus中执行，我开始在8i中不会有那条提示。
5，书中也会有错误，不可尽信~~
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本文源自TTT BLOG，原文地址：http://blog.chinaunix.net/u3/107265/showart_2201600.html