On Wed, 2013-04-17 at 16:58 +0100, Greg Stark wrote:
> On Wed, Apr 17, 2013 at 4:28 PM, Florian Pflug <fgp@phlo.org> wrote:
> > Is there any way we can change the checksum algorithm in 9.4
> > *without* breaking pg_upgrade?
>
> Personally I think we're going to need a solution for page format
> changes someday eventually....
>
> What advantages are we postponing now to avoid it?
>
> * 32-bit checksums?
> * Being able to enable/disable checksums?
>
> Anything else?
I'm not sure that changing the page format is the most difficult part of
enabling/disabling checksums. It's easy enough to have page header bits
if the current information is not enough (and those bits were there, but
Heikki requested their removal and I couldn't think of a concrete reason
to keep them).
Eventually, it would be nice to be able to break the page format and
have more space for things like checksums (and probably a few other
things, maybe some visibility-related optimizations). But that's a few
years off and we don't have any real plan for that.
What I wanted to accomplish with this patch is the simplest checksum
mechanism that we could get that would be fast enough that many people
would be able to use it. I expect it to be useful until we do decide to
break the page format.
Regards,Jeff Davis