Re: Add semi-join pushdown to postgres_fdw

From: Alexander Pyhalov <a(dot)pyhalov(at)postgrespro(dot)ru>
To: Alexander Korotkov <aekorotkov(at)gmail(dot)com>
Cc: Robins Tharakan <tharakan(at)gmail(dot)com>, Tomas Vondra <tomas(dot)vondra(at)enterprisedb(dot)com>, "Fujii(dot)Yuki(at)df(dot)MitsubishiElectric(dot)co(dot)jp" <Fujii(dot)Yuki(at)df(dot)mitsubishielectric(dot)co(dot)jp>, Ashutosh Bapat <ashutosh(dot)bapat(dot)oss(at)gmail(dot)com>, Pgsql Hackers <pgsql-hackers(at)postgresql(dot)org>, Ian Lawrence Barwick <barwick(at)gmail(dot)com>, tndrwang(at)gmail(dot)com
Subject: Re: Add semi-join pushdown to postgres_fdw
Date: 2025-03-18 11:13:56
Message-ID: c266bb209089a93bdcd61f6c4a4bfb42@postgrespro.ru
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Alexander Korotkov писал(а) 2025-03-18 03:27:
> Hi, Robins!
>
> On Tue, Mar 18, 2025 at 2:20 AM Robins Tharakan <tharakan(at)gmail(dot)com>
> wrote:
>> On Mon, 4 Dec 2023 at 07:22, Alexander Korotkov <aekorotkov(at)gmail(dot)com>
>> wrote:
>> >
>> >
>> > Now, I think this looks good. I'm going to push this if no objections.
>>
>> After this commit, I began seeing an unexpected ERROR - see this
>> bug-report.
>> https://www.postgresql.org/message-id/18852-fb75b88160678f78%40postgresql.org
>
> Thank you for pointing.
> I'll check this in the next couple of days.
>

Hi.
It seems conditions, coming from semi-joins, are handled incorrectly
under left and right join. When deparsing left/right joins and there are
semi-joins in inner or outer part of the query, the corresponding part
is deparsed as subquery. And we can't refer subquery vars from above, so
just should not pull up the restrictinfos. The attached patch does
exactly this.
--
Best regards,
Alexander Pyhalov,
Postgres Professional

Attachment Content-Type Size
0001-Avoid-pulling-up-restrict-infos-from-subqueries.patch text/x-diff 5.4 KB

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