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Don Burleson Blog 







Oracle redo log corruption tips

Oracle Database Tips by Donald BurlesonJuly 27, 2015 - Updated 1/20/2016

Question:  I appear to have redo log corruption.  When when I try to start it it gives me the error:

ORA-01172: recovery of thread 1 stuck at block 25 of file 2
ORA-01151: use media recovery to recover block, restore backup if needed.

I think that the datafile that is corrupted is a redo log file, so is one of the redo log groups that is with the status "current" even that the database is in mount mode.

How do I repair redo log corruption?

Answer:  First, followthese staps to attempt a simple startup/recovery.

Next, perform a full backup of what you have now, before you proceed further.

Next, open a severity 1 service request on MOSC.  Check the oracle alert log & any trace files for more details regarding your message and datafile.

If the database is up and redo logs are available you could type RECOVER DATAFILE 2 and hit enter for now. If the database is hung, SHUTDOWN IMMEDIATE then STARTUP MOUNT, then RECOVER DATAFILE 2, then ALTER DATABASE OPEN. RECOVER DATABASE will check and recover all oracle datafiles and is fine too.

Once you are working with MOSC, they will assist you with techniques for repairing the corrupt data blocks.

When using undocumented parameters like _allow_resetlogs_corruption, YOU MUST do it WITH the assistance of Oracle tech support.

Oracle tech support may also be able to patch the corrupt blocks using the BBED utility.

Oracle Recovery with  _allow_resetlogs_corruption

Recovery of a database using the undocumented parameter _allow_resetlogs_corruption should be regarded as a last-ditch, emergency recovery scenario only, and should not be attempted until all other avenues of recovery have been exhausted.

Note that Oracle will not support a database that has been recovered using this method unless it is subsequently exported and rebuilt.

Essentially, using _allow_resetlogs_corruption forces the opening of the datafiles even if their SCNs do not match up; then, on the next checkpoint, the old SCN values are overwritten. This could leave the database in an unknown state as far as concurrency.

For additional information on handling corruption, see the BC expert notes on corruption and see MOSC Note 1088018.1 - Handling Oracle Database Corruption Issues.



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