RE: Snapshot Control File

  • To: <rlsmith@xxxxxxx>, "Oracle-L" <oracle-l@xxxxxxxxxxxxx>
  • Date: Tue, 16 Aug 2005 12:08:53 -0400

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



============================================
Snapshot Control File:
============================================
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@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx] 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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