Andrew Dunstan <and...@dunslane.net> writes: > This is why I suggested the standard deviation, and why I find it would > be more useful than just min and max. A couple of outliers will set the > min and max to possibly extreme values but hardly perturb the standard > deviation over a large number of observations.
Hm. It's been a long time since college statistics, but doesn't the entire concept of standard deviation depend on the assumption that the underlying distribution is more-or-less normal (Gaussian)? Is there a good reason to suppose that query runtime is Gaussian? (I'd bet not; in particular, multimodal behavior seems very likely due to things like plan changes.) If not, how much does that affect the usefulness of a standard-deviation calculation? regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers