Horton

Re: Asynchronous Append on postgres_fdw nodes.

Andrei Lepikhov <a.lepikhov@postgrespro.ru>

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From: "Andrey V. Lepikhov" <a.lepikhov@postgrespro.ru>
To: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Cc: etsuro.fujita@gmail.com, movead.li@highgo.ca, pgsql-hackers@lists.postgresql.org
Date: 2020-06-15T09:59:18Z
Lists: pgsql-hackers

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On 6/15/20 1:29 PM, Kyotaro Horiguchi wrote:
> Thanks for testing, but..
> 
> At Mon, 15 Jun 2020 08:51:23 +0500, "Andrey V. Lepikhov" <a.lepikhov@postgrespro.ru> wrote in
>> The patch has a problem with partitionwise aggregates.
>>
>> Asynchronous append do not allow the planner to use partial
>> aggregates. Example you can see in attachment. I can't understand why:
>> costs of partitionwise join are less.
>> Initial script and explains of the query with and without the patch
>> you can see in attachment.
> 
> I had more or less the same plan with the second one without the patch
> (that is, vanilla master/HEAD, but used merge joins instead).
> 
> I'm not sure what prevented join pushdown, but the difference between
> the two is whether the each partitionwise join is pushed down to
> remote or not, That is hardly seems related to the async execution
> patch.
> 
> Could you tell me how did you get the first plan?

1. Use clear current vanilla master.

2. Start two instances with the script 'frgn2n.sh' from attachment.
There are I set GUCs:
enable_partitionwise_join = true
enable_partitionwise_aggregate = true

3. Execute query:
explain analyze SELECT sum(parts.b)
	FROM parts, second
	WHERE parts.a = second.a AND second.b < 100;

That's all.

-- 
Andrey Lepikhov
Postgres Professional
https://postgrespro.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.