Re: Add min and max execute statement time in pg_stat_statement

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