From: Tom Lane <tgl@sss.pgh.pa.us>
To: Robert Haas <robertmhaas@gmail.com>
cc: Rushabh Lathia <rushabh.lathia@gmail.com>,
        Tomas Vondra <tomas.vondra@2ndquadrant.com>,
        Peter Eisentraut <peter.eisentraut@2ndquadrant.com>,
        David Rowley <david.rowley@2ndquadrant.com>,
        PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: crashes due to setting max_parallel_workers=0
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Comments: In-reply-to Robert Haas <robertmhaas@gmail.com>
	message dated "Mon, 27 Mar 2017 07:59:27 -0400"
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Date: Mon, 27 Mar 2017 09:54:13 -0400
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Robert Haas <robertmhaas@gmail.com> writes:
> On Mon, Mar 27, 2017 at 1:29 AM, Rushabh Lathia
> <rushabh.lathia@gmail.com> wrote:
>> But it seems a bit futile to produce the parallel plan in the first plac=
e,
>> because with max_parallel_workers=3D0 we can't possibly get any parallel
>> workers ever. I wonder why compute_parallel_worker() only looks at
>> max_parallel_workers_per_gather, i.e. why shouldn't it do:
>> parallel_workers =3D Min(parallel_workers, max_parallel_workers);
>> Perhaps this was discussed and is actually intentional, though.

> It was intentional.  See the last paragraph of
> https://www.postgresql.org/message-id/CA%2BTgmoaMSn6a1780VutfsarCu0LCr%3D=
CO2yi4vLUo-JQbn4YuRA@mail.gmail.com

Since this has now come up twice, I suggest adding a comment there
that explains why we're intentionally ignoring max_parallel_workers.

			regards, tom lane


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