Re: Enabling Checksums

On Wed, 2012-11-14 at 17:40 -0800, Jeff Davis wrote:
> I'll do another pass to make sure I update all of the comments, and try
> to self review it.

Updated patches attached (the TLI patch wasn't changed though, only the
main checksums patch).

Changes:
  * A lot of cleanup
  * More testing
  * Added check during pg_upgrade to make sure the checksum settings
match.
  * Fixed output of pg_resetxlog to include information about checksums.
  * fixed contrib/pageinspect, and included upgrade script for it
  * removed code to skip the page hole during the checksum calculation.
We can reconsider if we think performance will be a real problem.
  * I added the header bits back in, because we will need them when we
want to support enabling/disabling checksums when the system is online.

I also did quite a bit more testing, although it could use some
performance testing. I'll also probably do another review pass myself,
but I think it's in good shape.

Also, if performance of the checksum calculation itself turns out to be
a problem, we might consider modifying the algorithm to do multiple
bytes at a time.

One purpose of this patch is to establish the on-disk format for
checksums, so we shouldn't defer decisions that would affect that (e.g.
doing checksum calculation in larger chunks, ignoring the page hole, or
using a different scheme for the bits in the header).

Regards,
    Jeff Davis