RE: Snapshot Control File

From: <oracle-l-bounce_at_freelists.org>
Date: Tue, 16 Aug 2005 12:08:53 -0400
Message-ID: <B30C2483766F9342B6AEF108833CC84E0465D2A9@ecogenemld50.Org.Collegeboard.local>

Ron,

>>Is the snapshot control file ever needed during recovery?
Short and right answer is "no".
Read the definition of the (RMAN) "Snapshot Control File" below.

Generally I would consider the (RMAN) "Snapshot Control File" worthless as it knows *nothing* about the backup (sets) currently being completed/made
Meaning the last backup metadata is not *in* the "Snapshot Control File", as it was "snapped" before the back started/completed.

*HOWEVER* it is a copy of the controlfie at the beginning of your current backup and while it knows nothing about the current backup, it "still" has knowledge/metadata about all previous RMAN backups (not deleted, marked missing or obsolete by RMAN).

I can invision a scenario where I lost *ALL* controlfiles on disk and on tape *AND* I do not use a RMAN Recovery Catalog. I would try and use the last known available RMAN "Snapshot Control File" to restore my database from an *older* (than the Snapshot Control File) backup and recovery my database.

I have not tried this yet.

hth

Chris Marquez
Oracle DBA

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Snapshot Control File:

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A copy of a database's control file taken by Recovery Manager. RMAN uses the snapshot control file to read a consistent version of a control file when either resynchronizing the recovery catalog or backing up the control file. A snapshot control file is created by Recovery Manager using the same Oracle code that creates backup control files: ALTER DATABASE BACKUP CONTROL FILE TO 'location'. Determining the Snapshot Control File Location: When RMAN needs to resynchronize from a read-consistent version of the control file, it creates a temporary snapshot control file. The default name for the snapshot control file is port-specific. Use the set snapshot controlfile name command to change the name of the snapshot control file; subsequent snapshot control files that RMAN creates use the name specified in the command.

        For example, start RMAN and then enter: set snapshot controlfile name to '/oracle/dba/prod/snap_prod.ctl';  

-----Original Message-----
From: oracle-l-bounce_at_freelists.org
[mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Smith, Ron L. Sent: Monday, August 15, 2005 5:06 PM
To: Oracle-L
Subject: Snapshot Control File

Is the snapshot control file ever needed during recovery?

Thanks
Ron

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Received on Tue Aug 16 2005 - 11:11:09 CDT