Re: visibility maps and heap_prune

Bruce Momjian wrote:
> Pavan Deolasee wrote:
>> On Fri, Feb 26, 2010 at 8:19 AM, Bruce Momjian <bruce(at)momjian(dot)us> wrote:
>>
>>> Whatever happened to this? It was in the first 9.0 commitfest but was
>>> returned with feedback but never updated:
>>>
>>>
>> Though Alex did some useful tests and review, and in fact confirmed that the
>> VACUUM time dropped from 16494 msec to 366 msec, I somehow kept waiting for
>> Heikki's decision on the general direction of the patch and lost interest in
>> between. If we are still interested in this, I can work out a patch and
>> submit for next release if not this.
>
> OK, TODO added:
>
> Have single-page pruning update the visibility map
> * https://commitfest.postgresql.org/action/patch_view?id=75
>
> Hopefully Heikki can comment on this.

I think I was worried about the possible performance impact of having to
clear the bit in visibility map again. If you're frequently updating a
tuple so that HOT and page pruning is helping you, setting the bit in
visibility map seems counter-productive; it's going to be cleared soon
again by another UPDATE. That's just a hunch, though. Maybe the overhead
is negligible.

--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com