What DBA Should Do When Redo Log Failure Occurs In The Database ?
Redo Log Failure
When LGWR cannot write to a member of a group, Redo Log Failure occurs in the Database. In that case, these things are done in the Database.
The database marks that member as INVALID.
Writes an error message to the LGWR trace file.
Writes an error message to the database alert log to indicate the problem with the inaccessible files.
When a redo log member is not available then LGWR has a specific reaction. LGWR can successfully write to at least one member in a group –: LGWR writes to the available members of a group and ignores the unavailable members. LGWR cannot access the next group at a log switch because the group must be archived-: Database operation temporarily halts until the group becomes available or until the group is archived. All members of the next group are inaccessible to LGWR at a log switch because of media failure-: Oracle Database returns an error, and the database instance shuts down. Solution-: 1)- DBA may need to perform media recovery on the database from the loss of a redo log file. 2a)- If the database checkpoint has moved beyond the lost redo log, media recovery is not necessary, because the database has saved the data recorded in the redo log to the data files. DBA need only drop the inaccessible redo log group. 2b)- If the database did not archive the bad log, use ALTER DATABASE CLEAR LOGFILE UNARCHIVED to disable archiving before the log can be dropped. All members of a group suddenly become inaccessible to LGWR while it is writing to them-: Oracle Database returns an error and the database instance immediately shuts down. Solution-: DBA may need to perform media recovery. If the media containing the log is not actually lost—for example, if the drive for the log was inadvertently turned off--media recovery may not be needed. In this case, DBA need only turn the drive back on and let the database perform automatic instance recovery.