Hi! Updated patch is attached. I've updated comment of mcelem_array_contained_selec with more detailed description of probability distribution assumption. Also, I found that "rest" behavious should be better described by Poisson distribution, relevant changes were made.
On Tue, Jan 17, 2012 at 2:33 PM, Noah Misch <n...@leadboat.com> wrote: > > By "summary frequency of elements", do you mean literally P_0 + P_1 ... + > P_N? > If so, I can follow the above argument for "column && const" and "column <@ > const", but not for "column @> const". For "column @> const", selectivity > cannot exceed the smallest frequency among const elements. A number of > high-frequency elements will drive up the sum of the frequencies without > changing the true selectivity much at all. > Referencing to summary frequency is not really correct. It would be more correct to reference to number of element in "const". When there are many elements in "const", "column @> const" selectivity tends to be close to 0 and "column @> const" tends to be close to 1. Surely, it's true when elements have some kind of middle values of frequencies (not very close to 0 and not very close to 1). I've replaced "summary frequency of elements" by "number of elements". ------ With best regards, Alexander Korotkov.
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