Thread

Re: POC: Parallel processing of indexes in autovacuum

Daniil Davydov <3danissimo@gmail.com> — 2025-11-23T15:02:22Z

Hi,

On Sun, Nov 23, 2025 at 5:51 AM Sami Imseih <samimseih@gmail.com> wrote:
>
> > > nworkers has a double meaning. The return value of
> > > AutoVacuumReserveParallelWorkers
> > > is nreserved. I think this should be
> > >
> > > ```
> > > nreserved = AutoVacuumReserveParallelWorkers(nworkers);
> > > ```
> > >
> > > and nreserved becomes the authoritative value for the number of parallel
> > > workers after that point.
>
> I could not find this pattern being used in the code base.
> I think it will be better and more in-line without what we generally do
> and pass-by-reference and update the value inside
> AutoVacuumReserveParallelWorkers:
>
> ```
> AutoVacuumReserveParallelWorkers(&nworkers).
> ```

Maybe I just don't like functions with side effects, but this function will
have ones anyway. I'll add logic with passing by reference as you
suggested.

>
> >> ---
> >> { name => 'autovacuum_max_parallel_workers', type => 'int', context =>
> >> 'PGC_SIGHUP', group => 'VACUUM_AUTOVACUUM',
> >>   short_desc => 'Maximum number of parallel autovacuum workers, that
> >> can be taken from bgworkers pool.',
> >>   long_desc => 'This parameter is capped by "max_worker_processes"
> >> (not by "autovacuum_max_workers"!).',
> >>   variable => 'autovacuum_max_parallel_workers',
> >>   boot_val => '0',
> >>   min => '0',
> >>   max => 'MAX_BACKENDS',
> >> },
> >>
> >> Parallel vacuum in autovacuum can be used only when users set the
> >> autovacuum_parallel_workers storage parameter. How about using the
> >> default value 2 for autovacuum_max_parallel_workers GUC parameter?
>
> > Sounds reasonable, +1 for it.
>
> v15-0004 has an incorrect default value for `autovacuum_max_parallel_workers`.
> It should now be 2.
>
> +          Sets the maximum number of parallel autovacuum workers that
> +          can be used for parallel index vacuuming at one time. Is capped by
> +          <xref linkend="guc-max-worker-processes"/>. The default is 0,
> +          which means no parallel index vacuuming.

Thanks for noticing it! Fixed.

I am sending an updated set of patches.

--
Best regards,
Daniil Davydov