[Networker] Why Oracle incremental backup is as large as a full?

2007-05-02 17:58:52
Subject: [Networker] Why Oracle incremental backup is as large as a full?
From: George Sinclair <George.Sinclair AT NOAA DOT GOV>
Date: Wed, 2 May 2007 17:58:58 -0400
We had a problem a while back, and we never did figure out what was causing it, but our nightly incrementals on this Oracle database were always the same size as the previous full. There were some users on there testing things, but no indications from them that they were doing anything that would have caused this weirdness. The Oracle database was about 80 GB, and we were using NMO 4.2, Oracle release was 10g and NetWorker 7.2.2. The first full we ran was around 80 GB (8 save sets), but each incremental thereafter was also 80 GB (and 8 save sets) with no reported errors or any messages about no save sets with that name existing in the media database, etc. Basically, nothing to indicate anything was amiss other than the large sizes.
The NSR client resource specified the rman script as the saveset, and it
had the appropriate
nsrnmo script listed under the 'Backup command' field.

The full rman script used a backup command like this:
backup full filesperset 10 format 'FULL_%d_%U' database;

The incremental rman script used a backup command like this:
backup incremental level 1 cumulative filesperset 10 format 'INCR_CUM_%d_%U' database;
We finally took the database off line. Later when re-testing, we changed
the syntax of the
two rman scripts respectively to this:

backup as backupset incremental level 0 cumulative database;


backup as backupset incremental level 1 cumulative database;

We've not seen this behavior again.

I realize it's impossible for anyone to really troubleshoot this, but can anyone offer any plausible explanations for this behavior, assuming, of course, that back when this was happening, we
*really* were specifying the correct rman script and not the wrong one.

I'm wondering if maybe at some point we shut down the database, recovered a copy and then never ran another level full but kept running incrementals? Would that cause this behavior, say, if we'd somehow recovered maybe an older version? Maybe by not running another full after the recovery then every subsequent cumulative incremental thinks everything has changed?
Not saying we did that, but could have.



George Sinclair - NOAA/NESDIS/National Oceanographic Data Center
SSMC3 4th Floor Rm 4145       | Voice: (301) 713-3284 x210
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