Re: BUG #18343: Incorrect description in postgresql.conf for max_parallel_workers_per_gather

On Thu, Feb 15, 2024 at 8:55 AM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> PG Bug reporting form <noreply(at)postgresql(dot)org> writes:
> > In the default postgresql.conf that is generated, there are the following
> > lines:
>
> > #max_worker_processes = 8 # (change requires restart)
> > #max_parallel_workers_per_gather = 2 # taken from max_parallel_workers
> > <<<<<<<<<<<<<<<<<<<<<<<< THIS
> > #max_parallel_maintenance_workers = 2 # taken from max_parallel_workers
> > max_parallel_workers = 8 # maximum number of
> max_worker_processes that
> > # can be used in parallel
> operations
>
> > it indicates that the default value is taken from whatever
> > max_parallel_workers is.
>
> No, you're misreading it. There's no magic connection between these
> two settings. What the comment means to say is that the per-gather
> worker processes come out of a pool of at most max_parallel_workers
> processes. Perhaps another wording would be better, but we don't have
> a lot of space here --- any thoughts?
>
> max_parallel workers = 8 # allocated from max_worker_processes

max_parallel_*_workers = N # allocated from max_parallel_workers

or maybe "consumed from ..."

Or

max_parallel_*_workers = N # capped at max_parallel_workers

The last one turns a process-oriented description into a constraint, the
latter seems to fit better in a config file.

David J.