Re: Asynchronous Append on postgres_fdw nodes.

On 6/5/21 22:12, Stephen Frost wrote:
> * Etsuro Fujita (etsuro(dot)fujita(at)gmail(dot)com) wrote:
>> I think the user should be careful about this. How about adding a
>> note about it to the “Asynchronous Execution Options” section in
>> postgres-fdw.sgml, like the attached?
+1
> ... then again, it'd really be better if we could figure out a way to
> just do the right thing here. I haven't looked at this in depth but I
> would think that the overhead of async would be well worth it just about
> any time there's more than one foreign server involved. Is it not
> reasonable to have a heuristic where we disable async in the cases where
> there's only one foreign server, but have it enabled all the other time?
> While continuing to allow users to manage it explicitly if they want.
Bechmarking of SELECT from foreign partitions hosted on the same server,
i see results:

With async append:
1 partition - 178 ms; 4 - 263; 8 - 450; 16 - 860; 32 - 1740.

Without:
1 - 178 ms; 4 - 583; 8 - 1140; 16 - 2302; 32 - 4620.

So, these results show that we have a reason to use async append in the
case where there's only one foreign server.

--
regards,
Andrey Lepikhov
Postgres Professional