Re: Partial aggregates pushdown

On 2023-04-07 22:53:53 -0400, Bruce Momjian wrote:
> On Fri, Apr 7, 2023 at 10:44:09PM -0400, Tom Lane wrote:
> > Bruce Momjian <bruce(at)momjian(dot)us> writes:
> > > On Fri, Apr 7, 2023 at 09:55:00PM -0400, Tom Lane wrote:
> > >> Uh, what? Why would we not be able to tell from the remote server's
> > >> version number whether it has this ability?
> >
> > > The issue is not a mismatch of postgres_fdw versions but the extension
> > > versions and whether the partial aggregate functions exist on the remote
> > > side, e.g., something like a PostGIS upgrade.
> >
> > postgres_fdw has no business pushing down calls to non-builtin functions
> > unless the user has explicitly authorized that via the existing
> > whitelisting mechanism. I think you're reinventing the wheel,
> > and not very well.
>
> The patch has you assign an option at CREATE AGGREGATE time if it can do
> push down, and postgres_fdw checks that. What whitelisting mechanism
> are you talking about? async_capable?

extensions (string)

This option is a comma-separated list of names of PostgreSQL extensions that are installed, in compatible versions, on both the local and remote servers. Functions and operators that are immutable and belong to a listed extension will be considered shippable to the remote server. This option can only be specified for foreign servers, not per-table.

When using the extensions option, it is the user's responsibility that the listed extensions exist and behave identically on both the local and remote servers. Otherwise, remote queries may fail or behave unexpectedly.