ORA-38856: cannot mark instance UNNAMED_INSTANCE_2 (redo thread 2) as enabled

在昨天11.2.0.2 for Linux 数据库恢复过程中,把数据文件从asm复制到单节点机器中恢复,在resetlogs过程中报如下ORA-38856错误
SQL> alter database open resetlogs;
alter database open resetlogs
*
ERROR at line 1:
ORA-38856: cannot mark instance UNNAMED_INSTANCE_2 (redo thread 2) as enabled
ORA-38856 is the expected error during open database resetlogs when the set of enabled instances (redo threads) in the controlfile does not match the set of enabled instances (redo threads) in datafile checkpoint. This is expected behavior in a normal RAC restore/recover/open resetlogs situation.

这句话的意思是:数据库在resetlogs的时候发现控制文件中的redo threads和数据文件汇总的redo threads不一致,从而出现该问题.
在本次恢复中禁用了所有和thread 2相关参数,数据库依然报告错误,是因为数据库在异常恢复过程中需要读取节点2的redo信息,现在无法读取从而出现该错误.但是使用了_allow_resetlogs_corruption 之后还是报该错误,实在诡异.通过查询mos发现有类似Unpublished Bug 4355382 ORA-38856: FAILED TO OPEN DATABASE WITH RESETLOGS WHEN USING RAC BACKUP,虽然说该bug在10.2.0.3中修复,但是在异常恢复过程中,本着在风险可控的情况下,大胆尝试,继续使用_no_recovery_through_resetlogs,数据库正常resetlogs成功.
可以参考：RMAN Duplicate from RAC backup fails ORA-38856 (Doc ID 334899.1)

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