Horton

Re: [PATCHES] Full page writes improvement, code update

Simon Riggs <simon@2ndquadrant.com>

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From: "Simon Riggs" <simon@2ndquadrant.com>
To: "Richard Huxton" <dev@archonet.com>
Cc: "Zeugswetter Andreas ADI SD" <ZeugswetterA@spardat.at>, "Koichi Suzuki" <suzuki.koichi@oss.ntt.co.jp>, <josh@agliodbs.com>, <pgsql-hackers@postgresql.org>, <pgsql-patches@postgresql.org>
Date: 2007-03-30T11:21:29Z
Lists: pgsql-hackers 
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