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

От: Pavel Stehule
Тема: Re: bitmapscan test, no success, bs is not faster
Дата: ,
Msg-id: Pine.LNX.4.44.0504270751180.9477-100000@kix.fsv.cvut.cz
(см: обсуждение, исходный текст)
Ответ на: Re: bitmapscan test, no success, bs is not faster  (Tom Lane)
Список: pgsql-hackers

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  bitmapscan test, no success, bs is not faster  (Pavel Stehule, )
   Re: bitmapscan test, no success, again  (Pavel Stehule, )
   Re: bitmapscan test, no success, bs is not faster  (Tom Lane, )
    Re: bitmapscan test, no success, bs is not faster  (Oleg Bartunov, )
    Re: bitmapscan test, no success, bs is not faster  (Oleg Bartunov, )
    Re: bitmapscan test, no success, bs is not faster  (Pavel Stehule, )

On Tue, 26 Apr 2005, Tom Lane wrote:

> Pavel Stehule <> 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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