From: Tom Lane <tgl@sss.pgh.pa.us>
To: Etsuro Fujita <fujita.etsuro@lab.ntt.co.jp>
cc: Robert Haas <robertmhaas@gmail.com>,
        Pg Hackers <pgsql-hackers@postgresql.org>
Subject: Re: Oddity with parallel safety test for scan/join target in
 grouping_planner
In-reply-to: <5C85F24E.4050404@lab.ntt.co.jp>
References: <5C75303E.8020303@lab.ntt.co.jp>
 <CA+TgmobmV=Zw2OEJKUorJe=e+_fCzsvYErR6tXxTjCzK45x9RQ@mail.gmail.com>
 <5C7908B9.5070407@lab.ntt.co.jp> <24818.1552077419@sss.pgh.pa.us>
 <5C85DC65.2050409@lab.ntt.co.jp> <32401.1552277190@sss.pgh.pa.us>
 <5C85ED63.8000805@lab.ntt.co.jp> <1962.1552281261@sss.pgh.pa.us>
 <5C85F24E.4050404@lab.ntt.co.jp>
Comments: In-reply-to Etsuro Fujita <fujita.etsuro@lab.ntt.co.jp>
	message dated "Mon, 11 Mar 2019 14:29:50 +0900"
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-ID: <22067.1552315572.1@sss.pgh.pa.us>
Date: Mon, 11 Mar 2019 10:46:12 -0400
Message-ID: <22068.1552315572@sss.pgh.pa.us>
Precedence: bulk

Etsuro Fujita <fujita.etsuro@lab.ntt.co.jp> writes:
> (2019/03/11 14:14), Tom Lane wrote:
>> Seems to me it's the other way around: the final target would include
>> all functions invoked in the grouping target plus maybe some more.
>> So a non-parallel-safe grouping target implies a non-parallel-safe
>> final target, but not vice versa.

> I mean the final *scan/join* target, not the final target.

Oh, of course.  Yup, I was too tired last night :-(.  So this is
just a plan-quality problem not a wrong-answer problem.

However, I'd still argue for back-patching into v11, on the grounds
that this is a regression from v10.  The example you just gave does
produce the desired plan in v10, and I think it's more likely that
people would complain about a regression from v10 than that they'd
be unhappy because we changed it between 11.2 and 11.3.

			regards, tom lane