Re: [HACKERS] Block level parallel vacuum

On Wed, Nov 13, 2019 at 9:51 AM Dilip Kumar <dilipbalaut@gmail.com> wrote:
>
> + /*
> + * Since parallel workers cannot access data in temporary tables, parallel
> + * vacuum is not allowed for temporary relation.
> + */
> + if (RelationUsesLocalBuffers(onerel) && params->nworkers >= 0)
> + {
> + ereport(WARNING,
> + (errmsg("skipping vacuum on \"%s\" --- cannot vacuum temporary
> tables in parallel",
> + RelationGetRelationName(onerel))));
> + relation_close(onerel, lmode);
> + PopActiveSnapshot();
> + CommitTransactionCommand();
> + /* It's OK to proceed with ANALYZE on this table */
> + return true;
> + }
> +
>
> If we can not support the parallel vacuum for the temporary table then
> shouldn't we fall back to the normal vacuum instead of skipping the
> table.  I think it's not fair that if the user has given system-wide
> parallel vacuum then all the temp table will be skipped and not at all
> vacuumed then user need to again perform normal vacuum on those
> tables.
>

Good point.  However, I think the current coding also makes sense for
cases like "Vacuum (analyze, parallel 2) tmp_tab;".  In such a case,
it will skip the vacuum part of it but will perform analyze.  Having
said that, I can see the merit of your point and I also vote to follow
your suggestion and add a note to the document unless it makes code
look ugly.

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