On Tue, 2008-10-21 at 14:26 -0700, Josh Berkus wrote:
> Gianni,
>
> > me and Gabriele Bartolini have been working on Bitmap Indexes (BMI) in
> > the last weeks, with advice and guidance from Simon Riggs. We feel
> > that we are about to approach the point where it is appropriate to ask
> > for feedback from this list.
>
> The other major issue with the Bitmap index patch as it stood in 2007 was
> that performance just wasn't that much faster than a btree, except for
> specific corner cases. Otherwise, someone else would have been interested
> enough to pick it up and finish it.
That seems a strange comment - are you thinking of hash indexes? Do you
have references to these poor performance tests?
BMIs will be a win for indexes with high numbers of duplicate keys -
where btrees don't operate very well. OTOH I expect btrees to continue
to be very useful in places where many keys are unique or nearly unique.
Index creation was much faster and produced much smaller indexes than
btrees, when used in the right situations. Better use of memory and
reduction of I/O alone are important factors. Significantly smaller
indexes also allow more indexes to be built on a table, leading to
overall gains in performance.
-- Simon Riggs www.2ndQuadrant.comPostgreSQL Training, Services and Support