| From: | Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> |
|---|---|
| To: | "Jim C(dot) Nasby" <jnasby(at)pervasive(dot)com> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>, Hannu Krosing <hannu(at)skype(dot)net> |
| Subject: | Re: Is full_page_writes=off safe in conjunction with PITR? |
| Date: | 2006-04-17 21:14:37 |
| Message-ID: | 200604172114.k3HLEbj14338@candle.pha.pa.us |
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| Lists: | pgsql-hackers |
Jim C. Nasby wrote:
> On Mon, Apr 17, 2006 at 03:00:58PM -0400, Tom Lane wrote:
> > I've applied a patch for this. On reflection, the CHECKPOINT during
> > pg_start_backup was actually necessary for torn-page safety even without
> > full_page_writes off. The reason is that the torn-page risk occurs when
> > we write a page from shared memory, not when we modify it in memory.
> > Without a CHECKPOINT, a page modified just before pg_start_backup could
> > be dumped during the backup and then be saved in a torn state, even
> > though no WAL record for it is emitted anytime during the backup
> > procedure. So that comment's been wrong all along.
>
> Are you going to back-patch this? If I understand correctly current
> behavior could mean people using PITR may have invalid backups. In the
> meantime, perhaps we should send an email to -annouce recommending that
> folks issue a CHEKCPOINT; after pg_start_backup and before initiating
> the filesystem copy.
We are disabling full_page_writes for 8.1.4, so they should be fine.
--
Bruce Momjian http://candle.pha.pa.us
EnterpriseDB http://www.enterprisedb.com
+ If your life is a hard drive, Christ can be your backup. +
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