Andres Freund <and...@anarazel.de> writes: > On 2016-03-12 12:22:01 -0500, Tom Lane wrote: >> I wonder whether that's pathification per se.
> If you're interested enough, I've uploaded a dump of the schema relevant > table to http://anarazel.de/t/lineitem_95_96_plan.dump.gz I haven't dug into it, but I'll bet this is a case of add_path deciding that the GroupAgg plan is fuzzily the same cost and better sorted (ie, it produces *some* sort order, versus none for the hash), so it kicks the hash plan out. Again, that would not have happened with the old hard-wired cost comparisons in grouping_planner, because they considered no factors other than an exact cost comparison. > I've not yet looked deep enough to determine the root cause; I did > however notice that set enable_sort = false; yields a cheaper plan than > the default one, within the fuzz range (137.91..137.93 vs 138.43..139.02). Yeah, you're just forcing it to choose the hash plan again. But that's within the cost fuzz range, so it's a legitimate choice. 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