Re: WIP checksums patch

On Mon, 2012-10-01 at 10:22 -0700, Josh Berkus wrote:
> > I think that's OK, because it's still protected by the WAL CRC, and
> > there's no expectation that the checksum is correct in shared buffers,
> > and the correct checksum should be set on the next checkpoint. Just an
> > observation.
>
> We'd need to document that emphatically. Otherwise folks running on ZFS
> and/or FusionIO with atomic writes (and, in the future, BTRFS) will
> assume that they can turn "full_page_writes" off and checksums on, and
> clearly that won't work with the current code. I think that's an
> acceptable limitation, I just think we need to document it carefully,
> and maybe throw a warning if people start up in that configuration.

What situation are you concerned about here? I think that COW
filesystems should still be safe with full_page_writes off, right?

The checksum is calculated before every write, and the COW filesystems
do atomic writes, so the checksums should always be fine. What am I
missing?

Regards,
Jeff Davis