Re: Parallel heap vacuum

On Tue, Feb 25, 2025 at 9:59 AM Melanie Plageman
<melanieplageman(at)gmail(dot)com> wrote:
>
> On Mon, Feb 24, 2025 at 8:15 PM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
> >
> > What I can see from these results was that we might not benefit much
> > from parallelizing phase III, unfortunately. Although in the best case
> > the phase III got about 2x speedup, as for the total duration it's
> > about only 10% speedup. My analysis for these results matches what
> > John mentioned; phase III is already the fastest phase and accounts
> > only ~10% of the total execution time, and the overhead of shared
> > TidStore offsets the speedup of phase III.
>
> So, are you proposing to drop the patches for parallelizing phase III
> for now? If so, are you planning on posting a set of patches just to
> parallelize phase I? I haven't looked at the prelim refactoring
> patches to see if they have independent value. What do you think is
> reasonable for us to try and do in the next few weeks?

Given that we have only about one month until the feature freeze, I
find that it's realistic to introduce either one parallelism for PG18
and at least we might want to implement the one first that is more
beneficial and helpful for users. Since we found that parallel phase
III is not very efficient in many cases, I'm thinking that in terms of
PG18 development, we might want to switch focus to parallel phase I,
and then go for phase III if we have time.

Regards,

--
Masahiko Sawada
Amazon Web Services: https://aws.amazon.com