Re: [HACKERS] Block level parallel vacuum

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 and Regards
Mahendra Thalor
EnterpriseDB: http://www.enterprisedb.com