| From: | Alexander Korotkov <aekorotkov(at)gmail(dot)com> |
|---|---|
| To: | Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> |
| Cc: | pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Statistics and selectivity estimation for ranges |
| Date: | 2012-08-15 08:34:07 |
| Message-ID: | CAPpHfdsPCcCERxywysaYoPUjk3OE6dM9Mm_4Yr86OkAJsSfuHA@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Wed, Aug 15, 2012 at 12:14 PM, Heikki Linnakangas <
heikki(dot)linnakangas(at)enterprisedb(dot)com> wrote:
> Histogram of upper bounds would be both more
>> accurate and natural for some operators. However, it requires collecting
>> additional statistics while AFAICS it doesn't liberate us from having
>> histogram of range lengths.
>>
>
> Hmm, if we collected a histogram of lower bounds and a histogram of upper
> bounds, that would be roughly the same amount of data as for the "standard"
> histogram with both bounds in the same histogram.
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?
------
With best regards,
Alexander Korotkov.
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