Re: HOT is applied

On 9/20/07, 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.)

well, I ran your test on my box and here are the results:
pre hot:
run 1: 3617.641 ms
run 2: 5195.215 ms
run 3: 6760.449 ms
after vacuum:
run 1: 4171.362 ms
run 2: 5513.317 ms
run 3: 6884.125 ms
post hot:
run 1: Time: 7286.292 ms
run 2: Time: 7477.089 ms
run 3: Time: 7701.229 ms

those results aren't exactly terrible, and this case is highly artificial.

merlin