On Mon, Mar 3, 2025 at 1:28 AM Masahiko Sawada <sawada.mshk@gmail.com> wrote:
>
> On Tue, Feb 25, 2025 at 4:49 PM Masahiko Sawada <sawada.mshk@gmail.com> wrote:
> >
> > On Tue, Feb 25, 2025 at 2:44 PM Melanie Plageman
> > <melanieplageman@gmail.com> wrote:
> > >
> > > On Tue, Feb 25, 2025 at 5:14 PM Masahiko Sawada <sawada.mshk@gmail.com> wrote:
> > > >
> > > > 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.
> > >
> > > Okay, well let me know how I can be helpful. Should I be reviewing a
> > > version that is already posted?
> >
> > Thank you so much. I'm going to submit the latest patches in a few
> > days for parallelizing the phase I. I would appreciate it if you could
> > review that version.
> >
>
> I've attached the updated patches that make the phase I (heap
> scanning) parallel. I'll share the benchmark results soon.
>
I've attached the benchmark test results.
Overall, with the parallel heap scan (phase I), the vacuum got speedup
much. On the other hand, looking at each phase I can see performance
regressions in some cases:
First, we can see the regression on a table with one index due to
overhead of the shared TidStore. Currently, we disable parallel index
vacuuming if the table has only one index as the leader process always
takes one index. With this patch, we enable parallel heap scan even if
the parallel index vacuuming is disabled, ending up using the shared
TidStore. In the benchmark test, while the regression due to that
overhead is about ~25% the speedup by parallel heap scan is 50%~, so
the performance number is good overall. I think we can improve the
shared TidStore in the future.
Another performance regression I can see in the results is that heap
vacuum phase (phase III) got slower with the patch. It's weired to me
since I don't touch the code of heap vacuum phase. I'm still
investigating the cause.
Regards,
--
Masahiko Sawada
Amazon Web Services: https://aws.amazon.com
