Horton

Re: Asynchronous Append on postgres_fdw nodes.

Andrei Lepikhov <a.lepikhov@postgrespro.ru>

View thread View on postgr.es
From: Andrey Lepikhov <a.lepikhov@postgrespro.ru>
To: Etsuro Fujita <etsuro.fujita@gmail.com>
Cc: Kyotaro Horiguchi <horikyota.ntt@gmail.com>, Justin Pryzby <pryzby@telsasoft.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2021-05-07T10:35:50Z
Lists: pgsql-hackers 
On 6/5/21 14:11, Etsuro Fujita wrote:
> On Tue, Apr 27, 2021 at 3:57 PM Andrey V. Lepikhov
> <a.lepikhov@postgrespro.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?
Yes. I think, new solution will be better.

-- 
regards,
Andrey Lepikhov
Postgres Professional

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.