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

Thank you all for the clarification. I like David Johnston's suggestion of

# capped at max_parallel_workers


That clearly defines the constraint.

On Thu, Feb 15, 2024 at 11:10 AM David G. Johnston <
david.g.johnston@gmail.com> wrote:

> On Thu, Feb 15, 2024 at 8:55 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:
>
>> PG Bug reporting form <noreply@postgresql.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.
>
>