Subject: Re: crashes due to setting max_parallel_workers=0
To: David Rowley <david.rowley@2ndquadrant.com>,
 Rushabh Lathia <rushabh.lathia@gmail.com>
References: <6ecd6f17-0dcf-1de7-ded8-0de7db1ddc88@2ndquadrant.com>
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 <CAGPqQf2C6W8aNy9v9ZW2fJs+7p0MoBFfHEtXG8yypimGXTRUvw@mail.gmail.com>
 <CAKJS1f8x1ptsCidf2FpRXySUJfWLEMjSwxV8_kvozHFPQYaAow@mail.gmail.com>
Cc: Tomas Vondra <tomas.vondra@2ndquadrant.com>,
 PostgreSQL-development <pgsql-hackers@postgresql.org>,
 Robert Haas <robertmhaas@gmail.com>
From: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>
Organization: 2ndQuadrant
Message-ID: <b37482ff-6eac-ae1a-ea91-94e71247dce1@2ndquadrant.com>
Date: Sat, 25 Mar 2017 09:31:55 -0400
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On 3/25/17 09:01, David Rowley wrote:
> On 25 March 2017 at 23:09, Rushabh Lathia <rushabh.lathia@gmail.com> wrote:
>> Also another point which I think we should fix is, when someone set
>> max_parallel_workers = 0, we should also set the
>> max_parallel_workers_per_gather
>> to zero. So that way it we can avoid generating the gather path with
>> max_parallel_worker = 0.
> I see that it was actually quite useful that it works the way it does.
> If it had worked the same as max_parallel_workers_per_gather, then
> likely Tomas would never have found this bug.

Another problem is that the GUC system doesn't really support cases
where the validity of one setting depends on the current value of
another setting.  So each individual setting needs to be robust against
cases of related settings being nonsensical.

-- 
Peter Eisentraut              http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services


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