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Re: On-line backup and point-in-time recovery (PITR)

From: Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>
To: Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>
Cc: Enzo D'addario <enzo(at)pienetworks(dot)com>, pgsql-admin(at)postgresql(dot)org
Subject: Re: On-line backup and point-in-time recovery (PITR)
Date: 2005-08-19 03:13:39
Message-ID: 20050819031339.GA10533@surnet.cl (view raw or flat)
Thread:
Lists: pgsql-admin
On Thu, Aug 18, 2005 at 11:01:27PM -0400, Bruce Momjian wrote:
> Enzo D'addario wrote:

> > 2.What happens with any DB inserts, updates, deletes etc that occur
> > between the SELECT pg_start_backup() and the end of the tar?
> > They would be already logged in the WAL files and already applied in the
> > tarball, do they then get duplicated during log replay in the recover
> > process? 
> 
> No, the recovery is just like crash recovery and everything comes back
> clean, but you do have to recover to a time _after_ the end of the
> backup.  If you want to recover to a time during the backup you have to
> use the previous backup and xlog files.

One important detail is that the system is able to detect whether a
change registered in WAL was already applied to the data files or not.
So if it's already applied, it doesn't need to be applied again.

-- 
Alvaro Herrera (<alvherre[a]alvh.no-ip.org>)
"La naturaleza, tan frágil, tan expuesta a la muerte... y tan viva"

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