Re: Statistics and selectivity estimation for ranges

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От	Alexander Korotkov
Тема	Re: Statistics and selectivity estimation for ranges
Дата	20 августа 2012 г. 00:32:05
Msg-id	CAPpHfdta8WyDD1bA7-g6qDmoPOEC6dchiyOcysPfQMm+QfwafQ@mail.gmail.com обсуждение исходный текст
Ответ на	Re: Statistics and selectivity estimation for ranges (Heikki Linnakangas <heikki.linnakangas@enterprisedb.com>)
Ответы	Re: Statistics and selectivity estimation for ranges Re: Statistics and selectivity estimation for ranges
Список	pgsql-hackers

Дерево обсуждения

On Thu, Aug 16, 2012 at 4:40 PM, Heikki Linnakangas <heikki.linnakangas@enterprisedb.com> wrote:

On 15.08.2012 11:34, Alexander Korotkov wrote:
Ok, we've to decide if we need "standard" histogram. In some cases it can
be used for more accurate estimation of< and> operators.
But I think it is not so important. So, we can replace "standard" histogram
with histograms of lower and upper bounds?

Yeah, I think that makes more sense. The lower bound histogram is still useful for < and > operators, just not as accurate if there are lots of values with the same lower bound but different upper bound.

New version of patch.

* Collect new stakind STATISTIC_KIND_BOUNDS_HISTOGRAM, which is lower and upper bounds histograms combined into single ranges array, instead of STATISTIC_KIND_HISTOGRAM.

* Selectivity estimations for >, >=, <, <=, <<, >>, &<, &> using this histogram.

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