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

From: Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>
To: "Enzo D'addario" <enzo(at)pienetworks(dot)com>
Cc: pgsql-admin(at)postgresql(dot)org
Subject: Re: On-line backup and point-in-time recovery (PITR)
Date: 2005-08-19 03:01:27
Message-ID: 200508190301.j7J31Ru16769@candle.pha.pa.us (view raw or flat)
Thread:
Lists: pgsql-admin
Enzo D'addario wrote:
> Hi All,
> 
> I have a couple of questions regarding On-line backup and point-in-time
> recovery (PITR) in the postgres documentation:
> 
> 1.How is it that we can create a tar file of the PG Data directory
> whilst postgres is running?

Whe pg_xlog archived files contain information to recover any
inconsistency in the backup tar file.

> 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.

-- 
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman(at)candle(dot)pha(dot)pa(dot)us               |  (610) 359-1001
  +  If your life is a hard drive,     |  13 Roberts Road
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073

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