On 2025-Jul-14, Tom Lane wrote: > "Scott Mead" <[email protected]> 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/ -- Álvaro Herrera PostgreSQL Developer — https://www.EnterpriseDB.com/
