Re: [HACKERS] Block level parallel vacuum

On Thu, 28 Nov 2019 at 11:57, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>
> On Thu, Nov 28, 2019 at 4:10 PM Mahendra Singh <mahi6run(at)gmail(dot)com> wrote:
> >
> > On Thu, 28 Nov 2019 at 13:32, Masahiko Sawada <masahiko(dot)sawada(at)2ndquadrant(dot)com> wrote:
> >>
> >> On Wed, 27 Nov 2019 at 19:21, Mahendra Singh <mahi6run(at)gmail(dot)com> wrote:
> >> >
> >> >
> >> > Thanks for the re-based patches.
> >> >
> >> > On the top of v35 patch, I can see one compilation warning.
> >> >>
> >> >> parallel.c: In function ‘LaunchParallelWorkers’:
> >> >> parallel.c:502:2: warning: ISO C90 forbids mixed declarations and code [-Wdeclaration-after-statement]
> >> >> int i;
> >> >> ^
> >> >
> >> >
> >> > Above warning is due to one extra semicolon added at the end of declaration line in v35-0003 patch. Please fix this in next version.
> >> > + int nworkers_to_launch = Min(nworkers, pcxt->nworkers);;
> >>
> >> Thanks. I will fix it in the next version patch.
> >>
> >> >
> >> > I will continue my testing on the top of v35 patch set and will post results.
> >
> >
> > While reviewing v35 patch set and doing testing, I found that if we disable leader participation, then we are launching 1 less parallel worker than total number of indexes. (I am using max_parallel_workers = 20, max_parallel_maintenance_workers = 20)
> >
> > For example: If table have 3 indexes and we gave 6 parallel vacuum degree(leader participation is disabled), then I think, we should launch 3 parallel workers but we are launching 2 workers due to below check.
> > + nworkers = lps->nindexes_parallel_bulkdel - 1;
> > +
> > + /* Cap by the worker we computed at the beginning of parallel lazy vacuum */
> > + nworkers = Min(nworkers, lps->pcxt->nworkers);
> >
> > Please let me know your thoughts for this.

Thanks!

> I think it is probably because this part of the code doesn't consider
> PARALLEL_VACUUM_DISABLE_LEADER_PARTICIPATION. I think if we want we
> can change it but I am slightly nervous about the code complexity this
> will bring but maybe that is fine.

Right. I'll try to change so that.

Regards,

--
Masahiko Sawada http://www.2ndQuadrant.com/
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