Re: Checksums and full_page_writes

On Fri, Dec 26, 2014 at 04:07:11PM -0500, Bruce Momjian wrote:
> On Fri, Dec 26, 2014 at 01:11:57PM +0300, Borodin Vladimir wrote:
> > Hi all.
> >
> > I ve read thread [0], src/backend/storage/page/README and everything I found in
> > the documentation about checksums [1, 2] but I haven t understood what is my
> > risk if I enable checksums during initdb and turn off full_page_writes?
> >
> > Am I right that I can get torn pages on disk in that case but I will somehow
> > know about it during checksum checking when this page will be read from disk to
> > shared buffers? And is there any way to recover such torn page (from replica or
>
> Yes.
>
> > backup+archived logs, for example)?
>
> There is no way to _fix_ the torn page, but you can ignore the error
> with ignore_checksum_failure:
>
>     http://www.postgresql.org/docs/9.4/static/runtime-config-developer.html

Oh, you can fail-over to the replica, of course, but there is no clean
way to restore just the torn page.

--
  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

  + Everyone has their own god. +