Re: Parallel heap vacuum

On Tue, Mar 11, 2025 at 5:00 AM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
>
> On Sun, Mar 9, 2025 at 11:28 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> >
> >
> > Does phase 3 also use parallelism? If so, can we try to divide the
> > ring buffers among workers or at least try vacuum with an increased
> > number of ring buffers. This would be good to do for both the phases,
> > if they both use parallelism.
>
> No, only phase 1 was parallelized in this test. In parallel vacuum,
> since it uses (ring_buffer_size * parallel_degree) memory, more pages
> are loaded during phase 1, increasing cache hits during phase 3.
>

Shouldn't we ideally try with a vacuum without parallelism with
ring_buffer_size * parallel_degree to make the comparison better?
Also, what could be the reason for the variation in data of phase-I?
Do you restart the system after each run to ensure there is nothing in
the memory? If not, then shouldn't we try at least a few runs by
restarting the system before each run to ensure there is nothing
leftover in memory?

--
With Regards,
Amit Kapila.