Oracle Hidden Parameter:_disable_logging

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Oracle Hidden Parameter:_disable_logging

作者：eygle |【转载时请以超链接形式标明文章出处和作者信息及本声明】
链接：http://www.eygle.com/archives/2005/10/oracle_hidden_disable_logging.html

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提示：Oracle的隐含参数只应该在测试环境或者在Oracle Support的支持下使用。
从Oracle的系统表中，我们知道Oracle存在一个隐含参数_disable_logging可以用于禁用日志生成，这个参数显然只能用于测试目的（可以极大提高Benchmark测试的性能），禁止日志生成必然导致事务的不可恢复性。

SQL> select ksppinm,ksppdesc from x$ksppi where ksppinm like '%logging';

KSPPINM              KSPPDESC
-------------------- ------------------------------
_disable_logging     Disable logging

因为特殊的需要，对这个参数进行了一点简单测试:

1.设置参数

[oracle@jumper bdump]$ sqlplus "/ as sysdba"

SQL*Plus: Release 9.2.0.4.0 - Production on Wed Oct 19 11:01:19 2005

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


Connected to:
Oracle9i Enterprise Edition Release 9.2.0.4.0 - Production
With the Partitioning option
JServer Release 9.2.0.4.0 - Production

SQL> alter system set "_disable_logging"=true scope=both;

System altered.

2.事务测试

SQL> create table t as select * from dba_users;

Table created.

SQL> select count(*) from t;

  COUNT(*)
----------
        12

SQL> shutdown abort;
ORACLE instance shut down.
SQL> startup
ORACLE instance started.

Total System Global Area   97588504 bytes
Fixed Size                   451864 bytes
Variable Size              33554432 bytes
Database Buffers           62914560 bytes
Redo Buffers                 667648 bytes
Database mounted.
Database opened.
SQL> select count(*) from t;
select count(*) from t
                     *
ERROR at line 1:
ORA-00942: table or view does not exist

由于未产生相应日志，数据库crash或shutdown abort之后，上一次成功完成的检查点之后变化的数据将无法恢复。

3.观察alert文件
从日志中我们可以看到在instance recovery中，没有数据被恢复，只有成功完成的上次检查点之前数据可以被获取，之后数据都将丢失。

Wed Oct 19 20:38:38 2005
Beginning crash recovery of 1 threads
Wed Oct 19 20:38:38 2005
Started first pass scan
Wed Oct 19 20:38:39 2005
Completed first pass scan
 0 redo blocks read, 0 data blocks need recovery
Wed Oct 19 20:38:39 2005
Started recovery at
 Thread 1: logseq 2, block 201, scn 0.897632464
Recovery of Online Redo Log: Thread 1 Group 1 Seq 2 Reading mem 0
  Mem# 0 errs 0: /opt/oracle/oradata/conner/redo01.log
Wed Oct 19 20:38:39 2005
Completed redo application
Wed Oct 19 20:38:39 2005
Ended recovery at
 Thread 1: logseq 2, block 201, scn 0.897652465
 0 data blocks read, 0 data blocks written, 0 redo blocks read
Crash recovery completed successfully

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By eygle on 2005-10-19 20:50 | Comments (1) | Posted to Internal | Edit |Pageviews:

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» 隐含参数_disable_logging的几点说明 from Friends Life and Oracle
在很久以前,曾经介绍过Oracle的一个内部隐含参数_disable_logging,看到有朋友论述这个参数,今天忍不住做一点补充说明. 1.当然,隐含有风险,设置请谨慎. 2.最初在9.2.0.6 Solaris版本上,设置该参数会触发Bug:3868748 使得数据库无法启动. 从警告日志中,通常可以获得的错误提示是: ORA-07445: exception encountered: core dump [kcrfwcint()+1625] [SIGFPE] [Integer divide b... [Read More]

Tracked on September 11, 2006 11:22 AM

留言 (1)

我倒是更想知道，可以极大提高Benchmark测试的性能，这个性能的提高有多少？
eygle能不能作个测试？

Posted by: kamus at October 21, 2005 4:22 PM

www.eygle.com

Oracle Hidden Parameter:_disable_logging

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