Re: On-disk bitmap index patch

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.

> Also, the bitmap index is very small in low cardinality cases, where the
> btree tends to take up at least 10 times more space.

Also, are adding/changing rows is more expensive with bitmaps than
btrees?

--  Bruce Momjian   bruce@momjian.us EnterpriseDB    http://www.enterprisedb.com
 + If your life is a hard drive, Christ can be your backup. +