On Mon, 24 Jul 2006, Bruce Momjian wrote: > Jie Zhang wrote: > > > IIRC they quoted the cardinality of 10000 as something that is still > > > faster than btree for several usecases. > > > > > > And also for AND-s of several indexes, where indexes are BIG, your btree > > > indexes may be almost as big as tables but the resulting set of pages is > > > small. > > > > Yeah, Hannu points it out very well -- the bitmap index works very well when > > columns have low cardinalities and AND operations will produce small number > > of results. > > What operations on columns of low cardinality produce a small number of > results? That seems contradictory.
WHERE a = 1 and b = 2 a = 1 may be 5% of the table and b = 2 may be 5% of the table but their intersection may be .001%. Luke: the URL you sent to the bitmap slides was internal to Greenplum. Would you be able to put them on a public site? Thanks, Gavin ---------------------------(end of broadcast)--------------------------- TIP 1: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly