Re: Is full_page_writes=off safe in conjunction with PITR?

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.
--
Jim C. Nasby, Sr. Engineering Consultant jnasby(at)pervasive(dot)com
Pervasive Software http://pervasive.com work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf cell: 512-569-9461