On Thu, 2007-02-01 at 23:57 -0600, Jim Nasby wrote:
> Has anyone actually measured the performance overhead of storing
> visibility info in indexes? I know the space overhead sounds
> daunting, but even if it doubled the size of the index in many cases
> that'd still be a huge win over having to scan the heap as well as
> the index (esp. for things like count(*)). There would also be
> overhead from having to update the old index tuple, but for the case
> of updates you're likely to need that page for the new index tuple
> anyway.
>
> I know this wouldn't work for all cases, but ISTM there are many
> cases where it would be a win.
It would prevent any optimization that sought to avoid inserting rows
into the index each time we perform an UPDATE. Improving UPDATE
performance seems more important than improving count(*), IMHO.
-- Simon Riggs EnterpriseDB http://www.enterprisedb.com