On Sat, Jul 18, 2020 at 12:44 AM Ashutosh Bapat <ashutosh.bapat....@gmail.com> wrote: > On Fri, Jul 17, 2020 at 8:24 PM Etsuro Fujita <etsuro.fuj...@gmail.com> wrote: > > On Fri, Jul 17, 2020 at 1:56 AM Alexey Kondratov > > <a.kondra...@postgrespro.ru> wrote: > > > However, there is an issue with aggregates as well. For a query like: > > > > > > SELECT > > > count(*) > > > FROM > > > documents > > > WHERE > > > company_id = 5; > > > > > > It would be great to teach planner to understand, that it's a > > > partition-wise aggregate as well, even without GROUP BY company_id, > > > which doesn't always help as well. I'll try to look closer on this > > > problem, but if you have any thoughts about it, then I'd be glad to > > > know. > > > > The reason why the aggregation count(*) isn't pushed down to the > > remote side is: 1) we allow the FDW to push the aggregation down only > > when the input relation to the aggregation is a foreign (base or join) > > relation (see create_grouping_paths()), but 2) for your case the input > > relation would be an append relation that contains the foreign > > partition as only one child relation, NOT just the foreign partition. > > The resulting Append path would be removed in the postprocessing (see > > [1]), but that would be too late for the FDW to do the push-down work. > > I have no idea what to do about this issue. > > Won't partitionwise aggregate push aggregate down to partition and > then from there to the foreign server through FDW?
Sorry, my words were not clear. The aggregation above is count(*) *without GROUP BY*, so we can’t apply PWA to it. Best regards, Etsuro Fujita
