Re: Statistics and selectivity estimation for ranges

On Wed, Mar 13, 2013 at 11:10 PM, Heikki Linnakangas <
hlinnakangas(at)vmware(dot)com> wrote:

> On 01.03.2013 16:22, Alexander Korotkov wrote:
>
>> On Tue, Mar 12, 2013 at 8:03 PM, Heikki Linnakangas<hlinnakangas(at)**
>> vmware.com <hlinnakangas(at)vmware(dot)com>
>>
>>> wrote:
>>>
>>
>> So, after some hacking, I ended up with this version. I find it more
>>> readable, I hope I didn't miss anything. This seems to produce results
>>> that
>>> are close, but not identical, to the original patch. I'm not sure where
>>> the
>>> discrepancy is coming from, or which patch is more correct in that
>>> respect.
>>> I'll continue from this tomorrow, but if you have the time, please take a
>>> look and let me know what you think.
>>>
>>
>> I've read your explanation and version of patch. In general it seems
>> correct to me.
>> There is one point why I have breaked up abstraction in some functions is
>> infinities. For example, in calc_length_hist_frac one or both of length1
>> and length2 can be infinity. In the line
>>
>>> frac = area / (length2 - length1);
>>>
>> you can get NaN result. I've especially adjusted the code to get more of
>> less correct result in this case.
>>
>
> Hmm, good point. I think I managed to fix those cases in the attached
> version. Is there any other corner case that I missed?
>

Did you try test case by Jeff Davis on this thread?
http://www.postgresql.org/message-id/1355167304.3896.37.camel@jdavis
I try it with attached version of patch and get NaN estimate.

------
With best regards,
Alexander Korotkov.