OK so we have a query that does OK in 8.4, goes to absolute crap in 9.2 and then works great in 9.3. Thing is we've spent several months regression testing 9.2 and no time testing 9.3, so we can't just "go to 9.3" in an afternoon. But we might have to. 9.2 seems hopelessly broken here. The query looks something like this: SELECT COUNT(*) FROM u, ug WHERE u.ugid = ug.id AND NOT u.d AND ug.somefield IN (SELECT somefunction(12345)); In 8.4 we get this plan http://explain.depesz.com/s/r3hF which takes ~5ms In 9.2 we get this plan http://explain.depesz.com/s/vM7 which takes ~10s In 9.3 we get this plan http://explain.depesz.com/s/Wub which takes ~0.35ms The data sets are identical, the schemas are identical. Making changes to random_page_cost, sequential_page_cost and various other tuning parameters don't make it any better. PG versions: 8.4.20, 9.2.8, 9.3.4 Adding a limit to the function DOES make 9.2 better, ala: SELECT COUNT(*) FROM u, ug WHERE u.ugid = ug.id AND NOT u.d AND ug.somefield IN (SELECT somefunction(12345) limit 199); If the limit is 200 the bad plan shows up again. Question, is this a known issue with 9.2? If so is it something that will one day be fixed or are we stuck with it? Is there a workaround to make it better? Note: I'd rather not have to compile 9.2 from source with a patch, but at this point that would be acceptable over "you're stuck with it". -- To understand recursion, one must first understand recursion.
