Re: Bitmap index scans use of filters on available columns

Hello,

At Fri, 6 Nov 2015 09:49:30 +0530, Amit Kapila <amit.kapila16@gmail.com> wrote in
<CAA4eK1L_5T-UYsQeMOrX54g3QeXGhhAk5YFmzZqu5MidzxzkRg@mail.gmail.com>
> Apart from other problems discussed, I think it could also lead to
> a performance penality for the cases when the qual condition is
> costly as evaluating such a qual against lot of dead rows would be a
> time consuming operation.  I am not sure, but I think some of the
> other well know databases might not have any such problems as
> they store visibility info inside index due to which they don't need to
> fetch the heap tuple for evaluating such quals.

I was junst thinking of the same thing. Can we estimate the
degree of the expected penalty using heap statistics? Of couse
not so accurate though.

regards,

-- 
Kyotaro Horiguchi
NTT Open Source Software Center