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From: Simon Riggs <simon@2ndquadrant.com>
To: Richard Huxton <dev@archonet.com>
Cc: Zeugswetter Andreas ADI SD <ZeugswetterA@spardat.at>
Cc: Koichi Suzuki <suzuki.koichi@oss.ntt.co.jp>
Cc: josh@agliodbs.com
Cc: pgsql-hackers@postgresql.org
Cc: pgsql-patches@postgresql.org
Subject: Re: [PATCHES] Full page writes improvement, code update
Date: Fri, 30 Mar 2007 12:21:29 +0100
Message-ID: <1175253689.4386.749.camel@silverbirch.site> (raw)
In-Reply-To: <460CE5FE.5050906@archonet.com>
References: <460886E8.6040907@oss.ntt.co.jp>
	<4609CAC3.7060008@oss.ntt.co.jp>
	<1175072848.4386.323.camel@silverbirch.site>
	<200703291145.28574.josh@agliodbs.com>
	<1175200117.4386.616.camel@silverbirch.site>
	<460C611E.6090800@oss.ntt.co.jp>
	<E1539E0ED7043848906A8FF995BDA57901E7B246@m0143.s-mxs.net>
	<1175249717.4386.716.camel@silverbirch.site>
	<460CE5FE.5050906@archonet.com>

On Fri, 2007-03-30 at 11:27 +0100, Richard Huxton wrote:

> Is that always true? Could the backup not pick up a partially-written 
> page? Assuming it's being written to as the backup is in progress. (We 
> are talking about when disk blocks are smaller than PG blocks here, so 
> can't guarantee an atomic write for a PG block?)

Any page written during a backup has a backup block that would not be
removable by Koichi's tool, so yes, you'd still be safe.

i.e. between pg_start_backup() and pg_stop_backup() we always use full
page writes, even if you are running in full_page_writes=off mode.

-- 
  Simon Riggs             
  EnterpriseDB   http://www.enterprisedb.com





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