测试下_disable_logging将对数据库产生的影响，由于是隐含参数，所以通过如下方法获取对这个参数的描述：
SQL> select ksppinm,ksppdesc from x$ksppi where ksppinm like '%logging'; KSPPINM KSPPDESC ------------------------------------ _disable_logging Disable logging
将其改为ture，也就是启用了不记录日志的方式：
SQL> alter system set "_disable_logging"=true scope=both; System altered.
创建一个，并模拟事务运行，生成大量的redo,
SQL> create table mm tablespace marvener as select * from dba_objects; Table created. SQL> insert into mm select * from dba_objects; 45167 rows created. SQL> / 45167 rows created.
此时模拟掉电，shutdown abort关闭数据库：
SQL> shutdown abort ORACLE instance shut down. SQL> startup ORACLE instance started. Total System Global Area 1610612736 bytes Fixed Size 2084296 bytes Variable Size 385876536 bytes Database Buffers 1207959552 bytes Redo Buffers 14692352 bytes Database mounted. ORA-00354: corrupt redo log block header ORA-00353: log corruption near block 81435 change 856029 time 01/30/2012 15:50:39 ORA-00312: online log 1 thread 1: '/u01/app/oracle/oradata/marven/redo01.log'
如上。可以发现数据库无法正常打开，并提示重做日志块头损坏，在告警中可见大量的告警，
即使通过Resetlogs方式打开数据库：
alter system set "_allow_resetlogs_corruption"=true scope=spfile; shutdown abort startup
数据库仍然会显然如下告警，并强制关闭实例：
SMON: enabling cache recovery Mon Jan 30 16:15:41 2012 Errors in file /u01/app/oracle/admin/marven/udump/marven_ora_2900.trc: ORA-00600: internal error code, arguments: [2662], [0], [855728], [0], [855937], [8388649], [], [] Mon Jan 30 16:15:42 2012 Errors in file /u01/app/oracle/admin/marven/udump/marven_ora_2900.trc: ORA-00600: internal error code, arguments: [2662], [0], [855728], [0], [855937], [8388649], [], [] Mon Jan 30 16:15:42 2012 Error 600 happened during db open, shutting down database USER: terminating instance due to error 600 Instance terminated by USER, pid = 2900 ORA-1092 signalled during: alter database open resetlogs... Mon Jan 30 16:16:34 2012
然而可以通过推进Oracle的SCN来解决此类问题:
增进SCN有几种常用方法，这里介绍其中2种:
1.通过immediate trace name方式(在数据库Open状态下)
alter session set events ‘IMMEDIATE trace name ADJUST_SCN level x’;
2.通过10015事件(在数据库无法打开，mount状态下)
alter session set events ‘10015 trace name adjust_scn level x’;
注:10015的推进级别有个计算算法，具体可以参考adjust的官方说明。
alter session set events '10015 trace name adjust_scn level 10'; SQL> alter database open; Database altered.
