Horton

Re: Asynchronous Append on postgres_fdw nodes.

Etsuro Fujita <etsuro.fujita@gmail.com>

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From: Etsuro Fujita <etsuro.fujita@gmail.com>
To: Konstantin Knizhnik <k.knizhnik@postgrespro.ru>
Cc: Kyotaro Horiguchi <horikyota.ntt@gmail.com>, Justin Pryzby <pryzby@telsasoft.com>, Andrey Lepikhov <a.lepikhov@postgrespro.ru>, "movead.li" <movead.li@highgo.ca>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2020-09-22T17:20:46Z
Lists: pgsql-hackers 
On Tue, Sep 22, 2020 at 9:52 PM Konstantin Knizhnik
<k.knizhnik@postgrespro.ru> wrote:
> On 20.08.2020 10:36, Kyotaro Horiguchi wrote:
> > Come to think of "complex", ExecAsync stuff in this patch might be
> > too-much for a short-term solution until executor overhaul, if it
> > comes shortly. (the patch of mine here as a whole is like that,
> > though..). The queueing stuff in postgres_fdw is, too.

> Looks like current implementation of asynchronous append incorrectly
> handle LIMIT clause:
>
> psql:append.sql:10: ERROR:  another command is already in progress
> CONTEXT:  remote SQL command: CLOSE c1

Thanks for the report (and patch)!

The same issue has already been noticed in [1].  I too think the cause
of the issue would be in the 0003 patch (ie, “the queueing stuff “ in
postgres_fdw), but I’m not sure it is really a good idea to have that
in postgres_fdw in the first place, because it would impact
performance negatively in some cases (see [1]).

Best regards,
Etsuro Fujita

[1] https://www.postgresql.org/message-id/CAPmGK16E1erFV9STg8yokoewY6E-zEJtLzHUJcQx%2B3dyivCT%3DA%40mail.gmail.com

Commits

  1. Improve comments for trivial_subqueryscan().

  2. Disable asynchronous execution if using gating Result nodes.

  3. Allow asynchronous execution in more cases.

  4. Doc: Further update documentation for asynchronous execution.

  5. Fix rescanning of async-aware Append nodes.

  6. Doc: Update documentation for asynchronous execution.

  7. Fix EXPLAIN ANALYZE for async-capable nodes.

  8. Minor code cleanup in asynchronous execution support.

  9. Adjust input value to WaitEventSetWait() in ExecAppendAsyncEventWait().

  10. Add support for asynchronous execution.