Ah. I think your result is explained by this 8.1.4 bug fix:
2006-05-18 14:57 tgl
* src/backend/optimizer/plan/createplan.c (REL8_1_STABLE): When a bitmap indexscan is using a partial index, it is necessary to include the partial index predicate in the scan's "recheck condition". Otherwise, if the scan becomes lossy for lack of bitmap memory, we would fail to enforce that returned rows satisfy the predicate. Noted while studying bug #2441 from Arjen van der Meijden.
IOW, once the bitmap goes lossy, we'd return *every* row on any page that the index fingered as having *any* relevant row.
Better press him a little harder. There are a lot of known bugs in 8.1.3, and not any very good reason not to update to a later 8.1.x.
As a really short-term measure, you could possibly avoid this bug by increasing work_mem enough that the bitmap doesn't get compressed.
regards, tom lane
I'll press as I can...thanks for pointing that out to me. How would I determine how much to increase work_mem by (or to) until then? Got a little couch potato? Check out fun summer activities for kids.
