Subject: Re: Point in Time Recovery
From: Simon Riggs <simon@2ndquadrant.com>
To: Bruce Momjian <pgman@candle.pha.pa.us>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, pgsql-hackers@postgresql.org
In-Reply-To: <200407132301.i6DN1fb16205@candle.pha.pa.us>
References: <200407132301.i6DN1fb16205@candle.pha.pa.us>
Content-Type: text/plain
Organization: 2nd Quadrant
Message-Id: <1089760888.17493.3347.camel@stromboli>
Mime-Version: 1.0
Date: Wed, 14 Jul 2004 00:21:28 +0100
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On Wed, 2004-07-14 at 00:01, Bruce Momjian wrote:
> Tom Lane wrote:
> > Simon Riggs <simon@2ndquadrant.com> writes:
> > > So the situation is: 
> > > - You must only stop recovery at a point in time (in the logs) after the
> > > backup had completed.
> > 
> > Right.
> > 
> > > No way to enforce that currently, apart from procedurally. Not exactly
> > > frequent, so I think I just document that and move on, eh?
> > 
> > The procedure that generates a backup has got to be responsible for
> > recording both the start and stop times.  If it does not do so then
> > it's fatally flawed.  (Note also that you had better be careful to get
> > the time as seen on the server machine's clock ... this could be a nasty
> > gotcha if the backup is run on a different machine, such as an NFS
> > server.)
> 
> OK, but procedurally, how do you correlate the start/stop time of the
> tar backup with the WAL numeric file names?

No need. You just correlate the recovery target with the backup file
times. Mostly, you'll only ever use your last backup and won't need to
fuss with the times.

Backup should begin with a CHECKPOINT...then wait for that to complete,
just to make the backup as current as possible.

If you want to start purging your archives of old archived xlogs, you
can use the filedate (assuming you preserved that on your copy to
archive - but even if not, they'll be fairly close).

Best regards, Simon Riggs