Oracle中临时表产生过量Redo的说明

javayestome

最近,在Oracle9i中你用过临时表吗?
它是否给你带来了性能提高?你注意过么?
好了言归正传.
我们知道临时表在DML操作中可以减少redo的生成,从而在保存中间结果集时可以带来较大的性能提高.
可是,如果你注意到了,在Oracle9i里,临时表可能比常规表还要产生更多的redo:
[oracle@jumper oracle]$ sqlplus eygle/eygle

SQL*Plus: Release 9.2.0.3.0 - Production on Sat Jul 3 16:37:01 2004

Copyright (c) 1982, 2002, Oracle Corporation.? All rights reserved.


Connected to:
Oracle9i Enterprise Edition Release 9.2.0.3.0 - Production ----请注意版本
With the Partitioning, OLAP and Oracle Data Mining options
JServer Release 9.2.0.3.0 - Production

SQL> create table ccc1? (c1 number);

Table created.

SQL> set autotrace trace stat
SQL> insert into ccc1 select rownum from dba_objects;
10468 rows created.


Statistics
----------------------------------------------------------
???????? 73? recursive calls
??????? 175? db block gets
????? 25623? consistent gets
???????? 36? physical reads
???? 157336? redo size --------------------常规表产生的redo,大约154K
??????? 622? bytes sent via SQL*Net to client
??????? 547? bytes received via SQL*Net from client
????????? 3? SQL*Net roundtrips to/from client
????????? 2? sorts (memory)
????????? 0? sorts (disk)
????? 10468? rows processed


SQL> create global temporary table ccc2 (c1 number) ;

Table created.

SQL> set autotrace trace stat
SQL> insert into ccc2 select rownum from dba_objects;

10468 rows created.


Statistics
----------------------------------------------------------
??????? 135? recursive calls
????? 10897? db block gets
????? 25653? consistent gets
??????? 115? physical reads
??? 1476012? redo size ---------------------这是临时表,产生了大约1.4M的redo
??????? 622? bytes sent via SQL*Net to client
??????? 547? bytes received via SQL*Net from client
????????? 3? SQL*Net roundtrips to/from client
????????? 2? sorts (memory)
????????? 0? sorts (disk)
????? 10468? rows processed

这使得在Oracle9i的这些版本中,使用临时表的意义不大了.
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今天down了个Oracle9205的patch,测试一下在Oracle9205中的情况:
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E:\Oracle\ora92\bin>sqlplus eygle/eygle SQL*Plus: Release 9.2.0.5.0 - Production on 星期六 7月 3 17:37:22 2004 Copyright (c) 1982, 2002, Oracle Corporation. All rights reserved. 连接到: Oracle9i Enterprise Edition Release 9.2.0.5.0 - Production ---注意版本 With the Partitioning, OLAP and Oracle Data Mining options JServer Release 9.2.0.5.0 - Production ?SQL> create table ccc1 (c1 number) tablespace eygle; 表已创建。 SQL> set autotrace trace stat SQL> insert into ccc1 select rownum from dba_objects; 已创建6188行。 Statistics ---------------------------------------------------------- 50 recursive calls 157 db block gets 3416 consistent gets 0 physical reads 92764 redo size --------------------------常规表大约产生90K的redo 611 bytes sent via SQL*Net to client 547 bytes received via SQL*Net from client 3 SQL*Net roundtrips to/from client 2 sorts (memory) 0 sorts (disk) 6188 rows processed SQL> drop table ccc1; 表已丢弃。 SQL> create global temporary table ccc2 (c1 number) ; 表已创建。 SQL> set autotrace trace stat SQL> insert into ccc2 select rownum from dba_objects; 已创建6188行。 Statistics ---------------------------------------------------------- 9 recursive calls 87 db block gets 3402 consistent gets 0 physical reads 16844 redo size -------------------------临时表这时只产生了16K的redo 614 bytes sent via SQL*Net to client 547 bytes received via SQL*Net from client 3 SQL*Net roundtrips to/from client 2 sorts (memory) 0 sorts (disk) 6188 rows processed SQL> 在9205中Oracle修正了这个bug.
如果你从来没有遇到这个bug，那么你是幸运的:)
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在buglist中，找到了以下说明:
2874489: Excessive REDO generated for INSERT as SELECT into GLOBAL TEMPORARY TABLES.
Fixed: 9205
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临时表终于回来了!
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2004年7月3日 星期六 17:53
If you have any question,please mail to eygle@itpub.net .
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