Ian Pye <ianpye(at)gmail(dot)com> writes:
> I'm trying to write a fdw where aggregate functions are pushed down to the
> underlaying data store.
> Is this possible?
Not yet. You can find various speculation about doing this in the
pgsql-hackers archives from the last month or so. It's going to require
some significant planner-infrastructure work, IMO, but we might have it
for 9.5.
regards, tom lane