Re: Backup on standby database

Hi Mark.

Restoring just a full backup is simpler because you don't have to wait for the restore of the incremental backups. However, you are right: I should have said "faster" not "simpler". Second, do you mean taking more than one backup per day? In that case, you maybe right, depending on the timing. Space for the daily full backup is not a problem if you have deduplication enabled. File space consumed is approximately the same as the incremental backup. Deduplication will take care of backing up only the blocks that are different from the previous backup. The snag is that not all deduplication algorithms work well with compression. However, those are the details specific to the particular backup software. For instance, Data Domain Boost works well with lzip compression but not with gzip which is used by rman. 

Lastly, backup and restore are always the last line of defense. The  first line is RAC, the second line is Data Guard and the last line is the backup. If you are in situation that you have to restore backup, you are already in trouble. In that case, I want to restore a full backup, because I must do that anyway, and apply all the archive logs for the period between the last log and the crash. The shorter the period between the last full backup and the crash, the faster the recovery will be. If you can backup the database within 4 hours,  you can even take 2 full backups per day. It doesn't matter, they're running off the standby anyway.

Regards

"You MUST restore the last full backup and all incremental backups taken after the last full. It is much simpler to restore only the last full backup and apply the logs."

Why is it simpler?  You just issue recover database and rman takes care of the rest.  it is not like you must manually figure out which incremental backups and archive logs you need to apply.

While I would prefer running level 0 backups daily where possible and may or may not use level 1 backups with them the only real cost of level 1 backups is the extra file space consumed by the level 1 backup that would not be consumed if you only ran archive logs backups to go along with your level 0 or full.  On systems with high update to the same rows use of level 1 backups can save a log of recovery time and time to recover is important.

Mark Powell

Database Administration

(313) 592-5148

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From: oracle-l-bounce_at_freelists.org <oracle-l-bounce_at_freelists.org> on behalf of Mladen Gogala <gogala.mladen_at_gmail.com>
Sent: Thursday, May 13, 2021 11:01 AM
To: Jared Still <jkstill_at_gmail.com>
Cc: Oracle-L Freelists <oracle-l_at_freelists.org>
Subject: Re: Backup on standby database

 

Well, it is not possible to recover DB from an incremental backup alone. You MUST restore the last full backup and all incremental backups taken after the last full. It is much simpler to restore only the last full backup and apply the logs. That is possible if you have daily full backups w/o any incremental backups. The problem with such strategy is storage, not the duration of the full backup which takes longer than the incremental. That doesn't matter since the standby is not open and is not doing anything for the end users. Nobody will suffer because you're running backup from standby. The storage problem can be resolved by deduplication. If the OP's backup software supports deduplication, and pretty much every backup suite does support it, his subsequent full backups will take as much space as an incremental.

On 5/13/21 10:01 AM, Jared Still wrote:

Hi Mladen,

Please explain:

Also, if you plan on running incremental backups, which I don't consider a good idea,

Jared Still
Certifiable Oracle DBA and Part Time Perl Evangelist

Principal Consultant at Pythian

Oracle ACE Alumni

Pythian Blog http://www.pythian.com/blog/author/still/

Github: https://github.com/jkstill

-- 
Mladen Gogala
Database Consultant
Tel: (347) 321-1217
https://dbwhisperer.wordpress.com

-- 
Mladen Gogala
Database Consultant
Tel: (347) 321-1217
https://dbwhisperer.wordpress.com