Re: VACUUM PARALLEL option vs. max_parallel_maintenance_workers

On Mon, 5 Oct 2020 at 11:21, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>
> On Sat, Oct 3, 2020 at 9:25 AM Masahiko Sawada
> <masahiko(dot)sawada(at)2ndquadrant(dot)com> wrote:
> > To make the behavior of parallel vacuum more consistent with other
> > parallel maintenance commands (i.g., only parallel INDEX CREATE for
> > now), as a second idea, can we make use of parallel_workers reloption
> > in parallel vacuum case as well?
>
> That seems like a terrible idea to me. I don't see why the number of
> workers that some user thinks should be used to perform a scan on the
> table as part of the query should be the same as the number of workers
> that should be used for a maintenance operation.

Agreed. But the same is true for parallel REINDEX? It's also a
maintenance operation.

In any case, the thing would get more complex if lazy vacuum or vacuum
full were to support parallel operation on table scan in the future.

Regards,

--
Masahiko Sawada http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services