Jeff Davis <pg...@j-davis.com> writes: > On Tue, 2009-02-24 at 00:18 -0500, Robert Haas wrote: >> It only took me about 5 minutes to come up with a test case against CVS >> HEAD where disabling index scans resulted in a significant dropoff in >> performance. Here it is:
> On the other hand, Teodor showed a typical use case and a very > substantial performance gain: Yeah. Whatever we do here is a tradeoff (and whether Robert likes it or not, reliability and code maintainability weigh heavily in the tradeoff). > I wonder how many people really use GIN with non-bitmap scans for some > benefit? And even if the benefit exists, does the planner have a way to > identify those cases reliably, or does it have to be done manually? A relevant point there is that most of the estimator functions for GIN-amenable operators are just smoke and mirrors; so if the planner is making a good choice between indexscan and bitmapscan at all, it's mostly luck. This might get better someday, but not in 8.4. regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers