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: "Andrey V. Lepikhov" <a.lepikhov@postgrespro.ru>
Cc: Kyotaro Horiguchi <horikyota.ntt@gmail.com>, Justin Pryzby <pryzby@telsasoft.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2021-04-27T12:31:08Z
Lists: pgsql-hackers 
On Mon, Apr 26, 2021 at 7:35 PM Andrey V. Lepikhov
<a.lepikhov@postgrespro.ru> wrote:
> Small mistake i found. If no tuple was received from a foreign
> partition, explain shows that we never executed node. For example,
> if we have 0 tuples in f1 and 100 tuples in f2:
>
> Query:
> EXPLAIN (ANALYZE, VERBOSE, TIMING OFF, COSTS OFF)
> SELECT * FROM (SELECT * FROM f1 UNION ALL SELECT * FROM f2) AS q1
> LIMIT 101;
>
> Explain:
>   Limit (actual rows=100 loops=1)
>     Output: f1.a
>     ->  Append (actual rows=100 loops=1)
>           ->  Async Foreign Scan on public.f1 (never executed)
>                 Output: f1.a
>                 Remote SQL: SELECT a FROM public.l1
>           ->  Async Foreign Scan on public.f2 (actual rows=100 loops=1)
>                 Output: f2.a
>                 Remote SQL: SELECT a FROM public.l2
>
> The patch in the attachment fixes this.

Thanks for the report and patch!  Will look into this.

Best regards,
Etsuro Fujita

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.