Re: crashes due to setting max_parallel_workers=0

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: Rushabh Lathia <rushabh(dot)lathia(at)gmail(dot)com>, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, Peter Eisentraut <peter(dot)eisentraut(at)2ndquadrant(dot)com>, David Rowley <david(dot)rowley(at)2ndquadrant(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: crashes due to setting max_parallel_workers=0
Date: 2017-03-27 13:54:13
Message-ID: 16476.1490622853@sss.pgh.pa.us
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Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> On Mon, Mar 27, 2017 at 1:29 AM, Rushabh Lathia
> <rushabh(dot)lathia(at)gmail(dot)com> wrote:
>> But it seems a bit futile to produce the parallel plan in the first place,
>> because with max_parallel_workers=0 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 = 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%3DCO2yi4vLUo-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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