Re: Asynchronous Append on postgres_fdw nodes.

[Andrey V. Lepikhov]

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.lepik...@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

frgn2n.sh
Description: application/shellscript