环境:RHEL 6.5(x86-64) + Oracle 11.2.0.4 声明:推进SCN属于非常规恢复范畴,不建议非专业人员操作,否则后果自负。 需求:我这里演示下推进SCN 10W数量级,实际需求推进多少可以根据ORA-600 [2662] [a] [b] [c] [d] [e]具体值来确认。
ARGUMENTS: Arg [a] Current SCN WRAP Arg [b] Current SCN BASE Arg [c] dependent SCN WRAP Arg [d] dependent SCN BASE Arg [e] Where present this is the DBA where the dependent SCN came from.
更多详情可参考: ORA-600 [2662] "Block SCN is ahead of Current SCN" (文档 ID 28929.1)
SYS@orcl> select current_scn||'' from v$database;
CURRENT_SCN||''
--------------------------------------------------------------------------------
4563483988
可以看到当前SCN是4563483988,我现在想推进SCN,在10w级别,也就是4563483988标红数字修改为指定值。
重新启动数据库到mount阶段:
SYS@orcl> shutdown abort
ORACLE instance shut down.
SYS@orcl> startup mount
ORACLE instance started.
Total System Global Area 1235959808 bytes
Fixed Size 2252784 bytes
Variable Size 788529168 bytes
Database Buffers 436207616 bytes
Redo Buffers 8970240 bytes
Database mounted.
我这里直接把十万位的"4"改为"9"了,相当于推进了50w左右: 说明:实验发现oradebug poke 推进的SCN值,既可以指定十六进制的0x11008DE74,也可以直接指定十进制的4563983988。
SYS@orcl> oradebug setmypid
Statement processed.
SYS@orcl> oradebug dumpvar sga kcsgscn_
kcslf kcsgscn_ [06001AE70, 06001AEA0) = 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 6001AB50 00000000
SYS@orcl> select to_char(checkpoint_change#, 'XXXXXXXXXXXXXXXX') from v$database;
TO_CHAR(CHECKPOINT_CHANGE#,'XXXXXX
----------------------------------
110013C41
SYS@orcl> oradebug poke 0x06001AE70 8 4563983988
BEFORE: [06001AE70, 06001AE78) = 00000000 00000000
AFTER: [06001AE70, 06001AE78) = 1008DE74 00000001
SYS@orcl> oradebug dumpvar sga kcsgscn_
kcslf kcsgscn_ [06001AE70, 06001AEA0) = 1008DE74 00000001 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 6001AB50 00000000
SYS@orcl> alter database open;
Database altered.
SYS@orcl> select current_scn||'' from v$database;
CURRENT_SCN||''
--------------------------------------------------------------------------------
4563984271
可以看到已经成功将SCN推进到4563983988,SCN不断增长,所以这里查到的值略大一些。
本文在 2018-12-16 进一步补充说明:
在实际这类工作中,我们实际应该是要认真计算好需要推进SCN的值,而不应图省事直接给一个很大的值。后者不但是技术水平不成熟的表现,而且是不负责任的行为。
--ORA-00600: internal error code, arguments: [2662], [2], [1424107441], [2], [1424142235], [8388617], [], []
select 2*power(2,32)+1424142235 from dual;
10014076827
--ORA-00600: internal error code, arguments: [2662], [2], [1424142249], [2], [1424142302], [8388649], [], []
select 2*power(2,32)+1424143000 from dual;
10014077592
总结公式:c * power(2,32) + d {+ 可适当加一点,但不要太大!} c代表:Arg [c] dependent SCN WRAP d代表:Arg [d] dependent SCN BASE
oradebug setmypid
oradebug dumpvar sga kcsgscn_
oradebug poke 0x060012658 8 10014077592
oradebug dumpvar sga kcsgscn_
alter database open;
最后要说的是,做事情还是多考虑些,在非常规恢复中也能温柔的去推进SCN,高级DBA的价值从细节上体现。