Message-ID: <48F5D6AE.3000601@lelarge.info>
Date: Wed, 15 Oct 2008 13:40:30 +0200
From: Guillaume Lelarge <guillaume@lelarge.info>
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To: Ivan Voras <ivoras@freebsd.org>
CC: pgsql-performance@postgresql.org
Subject: Re: Backup strategies
References: <48F4D693.9000304@lerner.co.il> <gd4d7q$3ed$1@ger.gmane.org>
	<48F5BBFC.80404@krogh.cc> <gd4gp6$f4p$1@ger.gmane.org>
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Ivan Voras a écrit :
> Jesper Krogh wrote:
>>[...]
>> It worked when I tested it, but I may just have been darn lucky.
> 
> No, it should be ok - I just didn't catch up with the times :) At least
> that's my interpretation of this paragraph in documentation:
> 
> """Some backup tools that you might wish to use emit warnings or errors
> if the files they are trying to copy change while the copy proceeds.
> This situation is normal, and not an error, when taking a base backup of
> an active database; so you need to ensure that you can distinguish
> complaints of this sort from real errors..."""
> 
> It looks like PostgreSQL freezes the state of the "data" directory in
> this case (and new data goes only to the transaction log - pg_xlog),
> which effectively creates an application-level snapshot. Good to know.
> 

Nope. Even files in data directory change. That's why the documentation
warns against tools that emit errors for files that change during the copy.


-- 
Guillaume.
 http://www.postgresqlfr.org
 http://dalibo.com