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Re: bitmapscan test, no success, bs is not faster

From: Pavel Stehule <stehule(at)kix(dot)fsv(dot)cvut(dot)cz>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: bitmapscan test, no success, bs is not faster
Date: 2005-04-27 06:27:02
Message-ID: Pine.LNX.4.44.0504270751180.9477-100000@kix.fsv.cvut.cz (view raw or flat)
Thread:
Lists: pgsql-hackers
On Tue, 26 Apr 2005, Tom Lane wrote:

> Pavel Stehule <stehule(at)kix(dot)fsv(dot)cvut(dot)cz> writes:
> > I tested bitmap scan and maybe I didnt find good examples, but with bitmap 
> > scan is slower than hashjoin. Only when I use non otiptimized SELECT bps 
> > was little bit faster. All my SELECTs are equal.
> 
> Bitmap scans can't possibly be any faster for cases where the indexscan
> only fetches one row, which is true of all your test cases AFAICS.

yes, it's true. I found some selects where the benefit of bitmap scans is 
more clearly. There is only one small problem - optimizer didn't 
have to choose plan with bitmap scan in my examples. 

Thank you for explication, 
Regards
Pavel Stehule


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