Re: Page Checksums

On Sun, Dec 18, 2011 at 10:14:38AM +0200, Heikki Linnakangas wrote:
> On 17.12.2011 23:33, David Fetter wrote:
> >What:
> >
> > Please find attached a patch for 9.2-to-be which implements page
> > checksums. It changes the page format, so it's an initdb-forcing
> > change.
> >
> >How:
> > In order to ensure that the checksum actually matches the hint
> > bits, this makes a copy of the page, calculates the checksum, then
> > sends the checksum and copy to the kernel, which handles sending
> > it the rest of the way to persistent storage.
> >...
> >If this introduces new failure modes, please detail, and preferably
> >demonstrate, just what those new modes are.
>
> Hint bits, torn pages -> failed CRC. See earlier discussion:
>
> http://archives.postgresql.org/pgsql-hackers/2009-11/msg01975.php

The patch requires that full page writes be on in order to obviate
this problem by never reading a torn page. Instead, copy of the page
has already hit storage before the torn write occurs.

Cheers,
David.
--
David Fetter <david(at)fetter(dot)org> http://fetter.org/
Phone: +1 415 235 3778 AIM: dfetter666 Yahoo!: dfetter
Skype: davidfetter XMPP: david(dot)fetter(at)gmail(dot)com
iCal: webcal://www.tripit.com/feed/ical/people/david74/tripit.ics

Remember to vote!
Consider donating to Postgres: http://www.postgresql.org/about/donate