Re: Open issues for HOT patch

Tom Lane wrote:
> Bruce Momjian <bruce(at)momjian(dot)us> writes:
> > Tom Lane wrote:
> >> But then what happens when you want to update a second tuple on the same
> >> page? None of our existing plan types release and reacquire pin if they
> >> don't have to, and I really doubt that we want to give up that
> >> optimization.
>
> > You will prune when you lock the page and at that point unless you got
> > enough room for both tuples I doubt trying just before the second tuple
> > is going to help.
>
> No, you're missing the point completely. If the free space on the page
> is, say, 1.5x the average tuple size, the code *won't* prune, and then
> it will be stuck when it goes to do the second tuple update, because
> there is no chance to reconsider the prune/no-prune decision after some
> space is eaten by the first update.

My point is that if you only do this for INSERT/UPDATE, you can prune
when you have less than enough room for 3-4 tuples, and if you add the
xmin of the earliest prune xact you can prune even more aggressively.

--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://www.enterprisedb.com

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