Re: Enabling Checksums

Bruce Momjian <bruce@momjian.us>

From: Bruce Momjian <bruce@momjian.us>

To: Jeff Davis <pgsql@j-davis.com>

Cc: Simon Riggs <simon@2ndQuadrant.com>, Ants Aasma <ants@cybertec.at>, Greg Smith <greg@2ndquadrant.com>, Heikki Linnakangas <hlinnakangas@vmware.com>, PostgreSQL-development <pgsql-hackers@postgresql.org>

Date: 2013-04-12T19:21:46Z

Lists: pgsql-hackers

On Fri, Apr 12, 2013 at 12:07:36PM -0700, Jeff Davis wrote:
> > (Attached patch is discussion only. Checking checksum in recovery
> > isn't coded at all.)
> 
> I like it.
> 
> A few points:
> 
> * Given that setting the checksum is unconditional in a backup block, do
> we want to zero the checksum field when the backup block is restored if
> checksums are disabled? Otherwise we would have a strange situation
> where some blocks have a checksum on disk even when checksums are
> disabled.
> 
> * When we do PageSetChecksumInplace(), we need to be 100% sure that the
> hole is empty; otherwise the checksum will fail when we re-expand it. It
> might be worth a memset beforehand just to be sure.

Do we write the page holes to the WAL for full-page writes?  I hope we
don't.

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

  + It's impossible for everything to be true. +