Re: Disable parallel query by default

On Tue, Feb 10, 2026, at 4:45 AM, Álvaro Herrera wrote:
> On 2025-Jul-14, Tom Lane wrote:
>
> > "Scott Mead" <scott(at)meads(dot)us> writes:
> > > I'd like to re-open the discussion for this commitfest item. I
> > > still have not been able to find a value for parallel_setup_cost
> > > that makes good decisions about parallelism on a user's behalf. I
> > > believe that setting the SIGHUP-able max_parallel_workers_per_gather
> > > to 0 by default is still the best way to prevent runaway parallel
> > > execution behavior.
> >
> > I still think that proposal has no chance of getting off the ground.
> >
> > I do agree that the current default cost settings for parallel query
> > are over-optimistic and allow us to choose PQ when we shouldn't.
>
> This appears to have been the decision we took on this: we won't change
> the default; users affected by this can already turn
> max_parallel_workers_per_gather to 0; most users benefit from it being
> nonzero.
>
> What we could probably do, is improve the observability around parallel
> worker costs, so that people *know* that they need to do change the value.
> What do users need to pay attention to? Are there metrics we should
> expose?
>
> At this point I think we should mark this commitfest entry as rejected.
> https://commitfest.postgresql.org/patch/5751/

That's fair enough, interestingly, an article just popped-up on this last week: https://www.recall.ai/blog/postgres-postmaster-does-not-scale

>
> --
> Álvaro Herrera PostgreSQL Developer — https://www.EnterpriseDB.com/
>

--
Scott Mead
scott(at)meads(dot)us