Re: Oracle backup Problem.

There are two types of redo logs -- online and archived. They are used mainly to allow the database to recover to the point in time of failure. For example if you issue a "shutdown abort" command, or if you trip over the power cord to your database server, Oracle will automatically read the redo log files it needs to bring the database back to the state it was in when it failed. (The reason it needs to do this is because every change you make gets written to a redo file on disk, but not necessarily to the data files on disk. Those writes may be cached for performance reasons.)

The online redo logs do not need to be filled to be archived, but they do need to be archived before they can be backed up (if your database is open). If you want to backup your online redo logs every two hours (not sure why) you can force one log switch for each online redo log group you have in your database. Its either an alter system or an alter database command... I can't remember. Anyway, once the switches occur, the online redo logs will be archived. Note that this doesn't happen immediately. You need to check its status in the V$ tables (again, can't remember which one. V$LOG or V$LOGFILES ?) Ok, good luck.

• Matt

P.S. It might be worth while to browse through the INIT.ORA parameters regarding online redo logs. There may be a parameter you can set to force a log switch every two hours.

P.P.S. I also would look into the performance implications of performing a log switch. If the database checkpoints, you may be emptying caches and slowing your server down. For that reason, I know several DBAs who try to size their online redo logs so that they switch about once per day. I guess the rationale is that if your online redo logs go.

P.P.P.S. Sorry, not trying to be cute. I just keep remembering stuff -- Oracle will automatically mirror your online redo logs if you set it up to do so. You can put several log files into a single log group. This may be an alternative to backing them up every two hours.

Sanjay Narayanan wrote in message ...
>Hi Thiru,
>
>Thank you for the reply....
>Presently we are now taking full backups of the database once a day.
>
>And also i didn't understand exactly what archieved logs does.
>that is if the redo logs doesn't get filled will it still empty itself to
>the archieve logs and if so when?
>actually i want the backup of redo logs every 2 hrs even if doesn't get
>filled.
>
>Is that possible..Please help me.
>Again thank you for your reply.
>
>Sanjay.
>
>Thirumurugan vadivelu wrote in message
><3756F612.1A5CD577_at_infonautics.com>...
>>Hi
>>First of all You need to determine if the Database needs to be Up and
>Running
>>24 * 7 .
>>If so, then you got two Backup Possibilities :
>>1. Operate the Database in ARCHIVELOG mode and Take Hotbackups.In this
Case
>>Another Oracle process called ARCH is started which copies the Filled
>Online
>>Redolog Files to a Location Specified by LOG_ARCHIVE_DEST (in
>init<sid>.ora).
>>You need to Backup the Archived Redolog files also b'cos they will be
>needed
>>for Media Recovery. Do not Copy the Online Redolog files in this Case. You
>need
>>to monitor the LOG_ARCHIVE_DEST Filesystem via automated process bc'os if
>it
>>becomes full, then the DB hangs .-
>>
>>2. Logical DB Backups using Oracle Export Utility . DB needs to be Up
>during
>>the Backup preferably without much of User transactions. This method
doesnt
>>provide for File Recovery. Supports 3 modes viz Database Full Export, User
>and
>>Table level Exports.
>>
>>If you can afford to have Downtime, then Full Databse Cold Backups can be
>>done.The Database can be operated either in Archivelog or NoArchivelog
>modes.
>>Generally I dont backup the Online Redolog files except when you want to
>Shift
>>the enitre DB onto a Different Host and bring it up without Recovery.
>>
>>-Thiru
>>
>>Ramgopal Madarapu wrote:
>>
>>> Hi.
>>>
>>> i'm new to oracle server dba. could anyone please help me with the
backup
>>> stratergy.
>>> presently i am taking the daily full backup of the database.i also want
>to
>>> backup redo logs.
>>> which is not possible i was told. as it dumps to the archieve logs .in
>the
>>> alert i can see
>>> two log files alternating between themselves.is it bcoz of daily full
>>> backup.
>>>
>>> please help...how to back up redo logs/archieve logs every two hours.
>>>
>>> its bit confusing from SQL server.
>>> thanks in advance....
>>>
>>> would appreciate your kind help..
>>>
>>> Sanjay
>>
>
>
Received on Fri Jun 04 1999 - 18:21:36 CDT