Re: Query plan good in 8.4, bad in 9.2 and better in 9.3

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.