On Wed, Mar 6, 2013 at 11:04 PM, Robert Haas <robertmhaas@gmail.com> wrote:
>> When we first talked about this feature for
>> 9.2, we were going to exclude hint bits from checksums, in order to
>> avoid this issue; what happened to that?
>
> I don't think anyone ever thought that was a particularly practical
> design. I certainly don't.
Really? I thought it was pretty much the consensus for a good while.
The main problem it ran into was that we kept turning up hint bits
that we didn't realize we had. Index line pointers turned out to have
hint bits, page headers have one, and so on. As long as it was just
the heap page per-tuple transaction hint bits it seemed plausible to
just skip them or move them all to a contiguous blocks. Once it
started to look like the checksumming code had to know about every
data structure on every page it seemed a bit daunting. But that wasn't
something we realized for quite a long time.
--
greg