On Tue, Sep 6, 2011 at 19:51, Tom Lane <t...@sss.pgh.pa.us> wrote: > Marti Raudsepp <ma...@juffo.org> writes: >> So it seems the more fundamental issue is that b=0 and b='0' >> conditions are normalized differently when b is smallint. > > That's not a "fundamental issue", if by that you mean that it's a bug to > be fixed.
That was a bad choice of words, I meant "fundamental reason". > I realized that that patch is no good because it will break estimation > for inner-indexscan cases, where the selectivity of a bitmap index might > legitimately be better than what you'd get from the restriction clauses > alone. Possibly we could adapt the idea to use in choose_bitmap_and, > but it'll take more thought. Anyway the conditions for triggering this kind of plan are rather obscure, so unless there is a simple solution, it's probably not worth fixing. You need a constant query WHERE expression and partial index that mixes b=0 and b='0' syntax, on a non-integer column. The workaround is also straightforward: be consistent how you write the expression. The planner will only choose such a plan when you have a fairly large heap and small indexes, so the heap scan is likely to dominate query time anyway. In the original query it was a matter of 66 ms (single bitmap scan) vs 82 ms (redundant bitmap scans) Regards, Marti -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
