From: | Andrew Dunstan <andrew(at)dunslane(dot)net> |
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To: | David Fetter <david(at)fetter(dot)org>, Peter Eisentraut <peter_e(at)gmx(dot)net> |
Cc: | David G Johnston <david(dot)g(dot)johnston(at)gmail(dot)com>, pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: Add min and max execute statement time in pg_stat_statement |
Date: | 2015-02-19 01:50:45 |
Message-ID: | 54E54175.8040303@dunslane.net |
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Lists: | pgsql-hackers |
On 02/18/2015 08:34 PM, David Fetter wrote:
> On Tue, Feb 17, 2015 at 08:21:32PM -0500, Peter Eisentraut wrote:
>> On 1/20/15 6:32 PM, David G Johnston wrote:
>>> In fact, as far as the database knows, the values provided to this
>>> function do represent an entire population and such a correction
>>> would be unnecessary. I guess it boils down to whether "future"
>>> queries are considered part of the population or whether the
>>> population changes upon each query being run and thus we are
>>> calculating the ever-changing population variance.
>> I think we should be calculating the population variance.
> Why population variance and not sample variance? In distributions
> where the second moment about the mean exists, it's an unbiased
> estimator of the variance. In this, it's different from the
> population variance.
>
Because we're actually measuring the whole population, and not a sample?
cheers
andrew
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