On Tue, Jul 30, 2024 at 11:34 AM Andrei Lepikhov <lepihov@xxxxxxxxx> wrote: > > Thanks for report. I see such cases frequently enough and the key > problem here is data skew, as you already mentioned. Extended statistics > doesn't help here. Also, because we can't estimate specific values > coming from the outer NestLoop - we can't involve MCV to estimate > selectivity of the population. That's the reason why the optimiser uses > ndistinct value. > What you can do? I see only one option - split the table to some > partitions where data will be distributed more or less uniformly. And > invent a criteria for pruning unnecessary partitions. > Of course, you can also try pg_hint_plan and force planner to use > MergeJoin or HashJoin in that suspicious case. Thanks for the reply, Andrei, and for the advice about partitioning. - Jon
