Re: Add min and max execute statement time in pg_stat_statement

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.

Cheers,
David.
--
David Fetter <david(at)fetter(dot)org> http://fetter.org/
Phone: +1 415 235 3778 AIM: dfetter666 Yahoo!: dfetter
Skype: davidfetter XMPP: david(dot)fetter(at)gmail(dot)com

Remember to vote!
Consider donating to Postgres: http://www.postgresql.org/about/donate