From: | Etsuro Fujita <etsuro(dot)fujita(at)gmail(dot)com> |
---|---|
To: | "Andrey V(dot) Lepikhov" <a(dot)lepikhov(at)postgrespro(dot)ru> |
Cc: | Kyotaro Horiguchi <horikyota(dot)ntt(at)gmail(dot)com>, Justin Pryzby <pryzby(at)telsasoft(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
Subject: | Re: Asynchronous Append on postgres_fdw nodes. |
Date: | 2021-05-06 09:11:01 |
Message-ID: | CAPmGK17JTeGJtKrW_xeRtbXaPBBEQy3+AcOdqcrM0fnHGmJVsw@mail.gmail.com |
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Lists: | pgsql-hackers |
On Tue, Apr 27, 2021 at 3:57 PM Andrey V. Lepikhov
<a(dot)lepikhov(at)postgrespro(dot)ru> wrote:
> One more question. Append choose async plans at the stage of the Append
> plan creation.
> Later, the planner performs some optimizations, such as eliminating
> trivial Subquery nodes. So, AsyncAppend is impossible in some
> situations, for example:
>
> (SELECT * FROM f1 WHERE a < 10)
> UNION ALL
> (SELECT * FROM f2 WHERE a < 10);
>
> But works for the query:
>
> SELECT *
> FROM (SELECT * FROM f1 UNION ALL SELECT * FROM f2) AS q1
> WHERE a < 10;
>
> As far as I understand, this is not a hard limit.
I think so, but IMO I think this would be an improvement rather than a bug fix.
> We can choose async
> subplans at the beginning of the execution stage.
> For a demo, I prepared the patch (see in attachment).
> It solves the problem and passes the regression tests.
Thanks for the patch! IIUC, another approach to this would be the
patch you proposed before [1]. Right?
I didn't have time to look at the patch in [1] for PG14. My apologies
for that. Actually, I was planning to return it when the development
for PG15 starts.
Sorry for the late reply.
Best regards,
Etsuro Fujita
[1] https://www.postgresql.org/message-id/7fe10f95-ac6c-c81d-a9d3-227493eb9055%40postgrespro.ru
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