Re: [HACKERS] Block level parallel vacuum

On Tue, Oct 29, 2019 at 12:37 PM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
>
> I realized that v31-0006 patch doesn't work fine so I've attached the
> updated version patch that also incorporated some comments I got so
> far. Sorry for the inconvenience. I'll apply your 0001 patch and also
> test the total delay time.
>

+ /*
+ * Generally index cleanup does not scan the index when index
+ * vacuuming (ambulkdelete) was already performed. So we perform
+ * index cleanup with parallel workers only if we have not
+ * performed index vacuuming yet. Otherwise, we do it in the
+ * leader process alone.
+ */
+ if (vacrelstats->num_index_scans == 0)
+ lazy_parallel_vacuum_or_cleanup_indexes(vacrelstats, Irel, nindexes,
+ stats, lps);

Today, I was thinking about this point where this check will work for
most cases, but still, exceptions are there like for brin index, the
main work is done in amvacuumcleanup function. Similarly, I think
there are few more indexes like gin, bloom where it seems we take
another pass over-index in the amvacuumcleanup phase. Don't you think
we should try to allow parallel workers for such cases? If so, I
don't have any great ideas on how to do that, but what comes to my
mind is to indicate that via stats (
IndexBulkDeleteResult) or via an indexam API. I am not sure if it is
acceptable to have indexam API for this.

Thoughts?

--
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com