Message-ID: <5C85F24E.4050404@lab.ntt.co.jp>
Date: Mon, 11 Mar 2019 14:29:50 +0900
From: Etsuro Fujita <fujita.etsuro@lab.ntt.co.jp>
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Subject: Re: Oddity with parallel safety test for scan/join target in
 grouping_planner
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 <5C85DC65.2050409@lab.ntt.co.jp> <32401.1552277190@sss.pgh.pa.us>
 <5C85ED63.8000805@lab.ntt.co.jp> <1962.1552281261@sss.pgh.pa.us>
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To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Robert Haas <robertmhaas@gmail.com>,
        Pg Hackers <pgsql-hackers@postgresql.org>
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(2019/03/11 14:14), Tom Lane wrote:
> Etsuro Fujita<fujita.etsuro@lab.ntt.co.jp>  writes:
>> (2019/03/11 13:06), Tom Lane wrote:
>>> Is that the only possible outcome?  Per Robert's summary quoted above,
>>> it seems like it might be possible for the code to decide that the final
>>> scan/join target to be parallel safe when it is not, leading to outright
>>> wrong answers or query failures.
>
>> Maybe I'm missing something, but I think that if the final scan/join
>> target is not parallel-safe, then the grouping target would not be
>> parallel-safe either, by the construction of the two targets, so I don't
>> think that we have such a correctness issue.
>
> 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.

Best regards,
Etsuro Fujita