suppose i have 3 online redo log groups with two members on each group. Suppose any group is corrupted, then how to find the the corrupted exact group??. How to find weather the data in online redo log file are weather written or not on disk (datafile), and if not written and i have enter the command as:
ALTER DATABASE CLEAR UNARCHIVED LOGFILE GROUP 3;
then the files not written on disk (datafile) are lost or not??
It is normally very easy to see which redo log is corrupted, because your alert log will be blasted with a stack of errors about it along the lines of:
Errors in file ... ...
ORA-00313: open failed for members of log group 5 of thread 1
ORA-00312: online log 5 thread 1: '...'
Errors in file ...
ORA-00353: log corruption near block 5671374 change 456456911323
ORA-00334: archived log: ...
Errors in file ...
ORA-16038 log %s sequence# %s cannot be archived
ORA-354 corrupt redo log block header
ORA-353 log corruption near block <num> change <str >time <str>
ORA-367 checksum error in log file header
ORA-368 checksum error in redo log block
but the exact file that is having the issue will be referenced. There is a bug (10086147) that should *not* impact *your* version, where the information was not put into the alert log, only the session trace, but it is still there somewhere.
Once you've cleared that logfile it is imperative that you take a full backup, because you now have a hole in your archive log stream.
Things can get more complicated if you have other things that are dependent on that redo (standby database, goldengate etc).
See MOS note 836986.1 for more details - but in those situations I'd be enlisting the help of Support.