Re: Partial aggregates pushdown

Fujii(dot)Yuki(at)df(dot)MitsubishiElectric(dot)co(dot)jp писал 2023-07-10 10:35:
> I have modified the program except for the point "if the version of
> the remote server is less than PG17".
> Instead, we have addressed the following.
> "If check_partial_aggregate_support is true and the remote server
> version is older than the local server
> version, postgres_fdw does not assume that the partial aggregate
> function is on the remote server unless
> the partial aggregate function and the aggregate function match."
> The reason for this is to maintain compatibility with any aggregate
> function that does not support partial
> aggregate in one version of V1 (V1 is PG17 or higher), even if the
> next version supports partial aggregate.
> For example, string_agg does not support partial aggregation in PG15,
> but it will support partial aggregation
> in PG16.
>

Hi.

1) In foreign_join_ok() should we set fpinfo->user if
fpinfo->check_partial_aggregate_support is set like it's done for
fpinfo->use_remote_estimate? It seems we can end up with fpinfo->user =
NULL if use_remote_estimate is not set.

2) It seeems we found an additional issue with original patch, which is
present in current one. I'm attaching a patch which seems to fix it, but
I'm not quite sure in it.

> We have not been able to add a test for the case where the remote
> server version is older than the
> local server version to the regression test. Is there any way to add
> such tests to the existing regression
> tests?
>

--
Best regards,
Alexander Pyhalov,
Postgres Professional