Databases Reference
In-Depth Information
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the only tool provided by Oracle that can protect you and preserve all committed transactions in the event you
lose all members of the current online redo log group is Oracle data guard implemented in Maximum protection Mode.
refer to MOs note 239100.1 for more details regarding Oracle data guard protection modes.
Note
The online redo log files are never backed up by an RMAN online backup or by a user-managed hot backup. If
you did back up the online redo log files, it would be meaningless to restore them. The online redo log files contain
the latest redo generated by the database. You would not want to overwrite current files from a backup with old
redo information. For a database in archivelog mode, the online redo log files contain the most recently generated
transactions that are required to perform a complete recovery.
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use the rMan
backup database plus archivelog
command to ensure your current online redo log files (of all
the threads) are switched and archived before and after the backup of the database.
Tip
Since RMAN doesn't back up online redo log files, you can't use RMAN to restore these critical files. Given their
criticality, we thought it was important to include a chapter on how to deal with failures with online redo log files. We
first start by detailing how to decide what to restore.
Determining a Course of Action
Problem
You've experienced a problem with your online redo log files and need to determine what shape they are in and what
action to take.
Solution
Follow these steps when dealing with online redo log file failures:
1.
Inspect the alert.log file to determine which online redo log files have experienced a
media failure.
2.
Query V$LOG and V$LOGFILE to determine the status of the log group and degree
of multiplexing.
3.
If there is still one functioning member of a multiplexed group, then see Recipe 14-2 for
details on how to fix a failed member(s).
4.
Depending on the status of the log group, use Table
14-1
to determine what action to take.
