Tom Lane wrote: > regression=# explain select * from (select * from onek a where expensive(0)) > ss1 join (select * from onek b where expensive(1)) ss2 using(unique1); > QUERY PLAN > > ------------------------------------------------------------------------------- > Result (cost=543.30..849.05 rows=19721 width=484) > One-Time Filter: (expensive(0) AND expensive(1)) > -> Merge Join (cost=543.30..849.05 rows=19721 width=484) > Merge Cond: (a.unique1 = b.unique1)
I note that the rowcount is not altered by the one-time filter. Is this an issue? I imagine the problem is not being able to estimate the number of rows that pass the filter. > -> Sort (cost=271.65..276.61 rows=1986 width=244) > Sort Key: a.unique1 > -> Seq Scan on onek a (cost=0.00..162.86 rows=1986 width=244) > -> Sort (cost=271.65..276.61 rows=1986 width=244) > Sort Key: b.unique1 > -> Seq Scan on onek b (cost=0.00..162.86 rows=1986 width=244) > (10 rows) I also wonder whether it wouldn't be better in this case to apply each filter to each arm of the merge join. -- Alvaro Herrera http://www.CommandPrompt.com/ The PostgreSQL Company - Command Prompt, Inc. ---------------------------(end of broadcast)--------------------------- TIP 5: don't forget to increase your free space map settings