On Sat, 7 Jan 2006, Greg Stark wrote:
> > "Qingqing Zhou" <[EMAIL PROTECTED]> writes: > > > For b1, it actually doesn't matter much though. With bitmap we definitely > > can give a better EXPLAIN numbers for seqscan only, but without the bitmap, > > we seldom make wrong choice of choosing/not choosing sequential scan. > > I think you have a more severe problem than that. > > It's not sequential scans that we have trouble estimating. > It's the index scans that are the problem. Exactly, we are saying the same thing. > > In other words, the difference between being in Postgres's buffer cache and > being in the filesystem cache, while not insignificant, isn't really relevant > to the planner since it affects sequential scans and index scans equally. The bitmap was proposed since I think it is time to use dominated shared_buffer size. Thus, if it is not in buffer cache, it is not in OS cache either. Regards, Qingqing ---------------------------(end of broadcast)--------------------------- TIP 6: explain analyze is your friend