Database Reference
In-Depth Information
The contents of the current online redo log files aren't archived until a log switch occurs. This means that if you
lose all members of the current online redo log file, you lose transactions. Listed next are several mechanisms you can
implement to minimize the chance of failure with the online redo log files:
•
Multiplex the groups.
•
If possible, never allow two members of the same group to share the same controller.
•
If possible, never put two members of the same group on the same physical disk.
•
Ensure that OS file permissions are set appropriately (restrictive, that only the owner of the
Oracle binaries has permissions to write and read).
•
Use physical storage devices that are redundant (i.e., RAID [redundant array of
inexpensive disks]).
•
Appropriately size the log files, so that they switch and are archived at regular intervals.
•
Consider setting the
ARCHIVE_LAG_TARGET
initialization parameter to ensure that the online
redo logs are switched at regular intervals.
■
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.
see 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 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 wouldn't want to overwrite them 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.
Displaying Online Redo Log Information
Use the
V$LOG
and
V$LOGFILE
views to display information about online redo log groups and corresponding members:
COL group# FORM 99999
COL thread# FORM 99999
COL grp_status FORM a10
COL member FORM a30
COL mem_status FORM a10
COL mbytes FORM 999999
--
SELECT
a.group#
,a.thread#
,a.status grp_status
,b.member member
,b.status mem_status
,a.bytes/1024/1024 mbytes
