Re: parallel vacuum comments

On Mon, Dec 6, 2021 at 10:17 AM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>
> On Fri, Dec 3, 2021 at 6:06 PM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
> >
> > On Fri, Dec 3, 2021 at 6:03 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> > >
> > > On Thu, Dec 2, 2021 at 6:01 PM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
> > > >
> > > > I've attached updated patches.
> > > >
> > >
> > > I have a few comments on v4-0001.
> >
> > Thank you for the comments!
> >
> > > 1.
> > > In parallel_vacuum_process_all_indexes(), we can combine the two
> > > checks for vacuum/cleanup at the beginning of the function
> >
> > Agreed.
> >
> > > and I think
> > > it is better to keep the variable name as bulkdel or cleanup instead
> > > of vacuum as that is more specific and clear.
> >
> > I was thinking to use the terms "bulkdel" and "cleanup" instead of
> > "vacuum" and "cleanup" for the same reason. That way, probably we can
> > use “bulkdel" and “cleanup" when doing index bulk-deletion (i.g.,
> > calling to ambulkdelete) and index cleanup (calling to
> > amvacuumcleanup), respectively, and use "vacuum" when processing an
> > index, i.g., doing either bulk-delete or cleanup, instead of using
> > just "processing" . But we already use “vacuum” and “cleanup” in many
> > places, e.g., lazy_vacuum_index() and lazy_cleanup_index(). If we want
> > to use “bulkdel” instead of “vacuum”, I think it would be better to
> > change the terminology in vacuumlazy.c thoroughly, probably in a
> > separate patch.
> >
>
> Okay.
>
> > > 2. The patch seems to be calling parallel_vacuum_should_skip_index
> > > thrice even before starting parallel vacuum. It has a call to find the
> > > number of blocks which has to be performed for each index. I
> > > understand it might not be too costly to call this but it seems better
> > > to remember this info like we are doing in the current code.
> >
> > Yes, we can bring will_vacuum_parallel array back to the code. That
> > way, we can remove the call to parallel_vacuum_should_skip_index() in
> > parallel_vacuum_begin().
> >
> > > We can
> > > probably set parallel_workers_can_process in parallel_vacuum_begin and
> > > then again update in parallel_vacuum_process_all_indexes. Won't doing
> > > something like that be better?
> >
> > parallel_workers_can_process can vary depending on bulk-deletion, the
> > first time cleanup, or the second time (or more) cleanup. What can we
> > set parallel_workers_can_process based on in parallel_vacuum_begin()?
> >
>
> I was thinking to set the results of will_vacuum_parallel in
> parallel_vacuum_begin().
>

This point doesn't seem to be addressed in the latest version (v6). Is
there a reason for not doing it? If we do this, then we don't need to
call parallel_vacuum_should_skip_index() from
parallel_vacuum_index_is_parallel_safe().

--
With Regards,
Amit Kapila.