Re: HOT is applied

Heikki Linnakangas wrote:
> Tom Lane wrote:
> > I've committed the HOT patch.
>
> Thanks, much easier to work with it now that it's in.
>
> > I'd still like to think about whether we
> > can be smarter about when to invoke pruning, but that's a small enough
> > issue that the patch can go in without it.
>
> Yeah. I'm doing some micro-benchmarking, and the attached test case is
> much slower with HOT. It's spending a lot of time trying to prune, only
> to find out that it can't.
>
> Instead of/in addition to avoiding pruning when it doesn't help, maybe
> we could make HeapTupleSatisfiesVacuum cheaper.
>
> I'm going to continue testing, this is just a heads-up that HOT as
> committed seriously hurts performance in some cases. (though one can
> argue that this test case isn't a very realistic one.)

This might be a simplistic question but if the page is +90% full and
there is a long-lived transaction, isn't Postgres going to try pruning
on each page read access?

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

+ If your life is a hard drive, Christ can be your backup. +