Re: performance of bitmap scans in nested loop joins

On Thu, 5 May 2005, Tom Lane wrote:

> "Sergey E. Koposov" <math(at)sai(dot)msu(dot)ru> writes:
> > And I coadded the "flat profiles" of first two (index scan) queries and
> > compared it with the flat profile of bitmap scan:
>
> Thanks, I had been thinking of doing that same calculation but hadn't
> got round to it yet. It looks like the bitmap case is actually a little
> ahead on buffer access (as you'd expect) and btree work (which is
> surprising because it ought to be dead even; are these numbers very
> repeatable?). Where we are losing is mostly on the actual manipulation

Yes, all those timings are rather stable and have been obtained on the very
unloaded system (and in fully cached regime).

With Best regards,
Sergey Koposov