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注意：Oracle的隱含參數只應該在測試環境或者在Oracle Support的支持下使用。

從Oracle的系統表中，我們知道Oracle存在一個隱含參數_disable_logging可以用于禁用日志生成，這個參數顯然只能用于測試目的（可以極大提高Benchmark測試的性能），禁止日志生成必然導致事務的不可恢復性,而且會導致日志文件損壞。

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

									KSPPINM    KSPPDESC

									-------------------- ------------------------------

									_disable_logging  Disable logging

因為特殊的需要，對這個參數進行了一點簡單測試:

1.設置參數

				?

									[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.事務測試

				?

									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

由于未產生相應日志，數據庫crash或shutdown abort之后，上一次成功完成的檢查點之后變化的數據將無法恢復。

3.觀察alert文件

從日志中我們可以看到在instance recovery中，沒有數據被恢復，只有成功完成的上次檢查點之前數據可以被獲取，之后數據都將丟失。

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									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