Peter Geoghegan <p...@bowt.ie> writes: > On Thu, Jun 1, 2017 at 8:40 AM, Tom Lane <t...@sss.pgh.pa.us> wrote: >> The thing that would actually have a chance of improving matters for Q20 >> would be if we could see our way to looking through the aggregation >> subquery and applying the foreign key constraint for lineitem. That >> seems like a research project though; it's surely not happening for v10.
> Do you mean teaching the optimizer to do something like this?: Uh, no. I don't think we want to add any run-time checks. The point in this example is that we'd get a better rowcount estimate if we noticed that the FK constraint could be considered while estimating the size of the partsupp-to-aggregated-subquery join. > Apparently selectivity estimation isn't particularly challenging with > the TPC-H queries. Maybe not with the rest of them, but we're certainly having an issue there with Q20. regards, tom lane -- Sent via pgsql-hackers mailing list (email@example.com) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers