* Jeff Janes (jeff.janes@gmail.com) wrote:
> On Wed, Oct 23, 2013 at 9:20 AM, Stephen Frost <sfrost@snowman.net> wrote:
> > * Josh Berkus (josh@agliodbs.com) wrote:
> > > On the other hand, it's still true that a high STDDEV indicates a high
> > > variance in the response times of a particular query, whereas a low one
> > > indicates that most are close to the average. While precision math
> > > might not work if we don't have the correct distribution, for gross DBA
> > > checks it's still useful. That is, I can answer the question in many
> > > cases of: "Does this query have a high average because of outliers, or
> > > because it's consisently slow?" by looking at the STDDEV.
> >
> > The concern is actually the reverse issue- often the question is "is
> > this query ever really slow?", or "when is this query really slow?" and
> > those questions are not answered by stddev, min, max, nor avg.
>
> How does max not answer "is this query ever really slow?"?
meh. max can end up being high for about a bazillion reasons and it'd
be difficult to really get any understanding of how or why it happened
from just that information.
> But good point,
> if we have a max, then I think a time-stamp for when that max was obtained
> would also be very useful.
And now we're getting into exactly what I was trying to suggest
up-thread: outlier detection and increased logging when a rare event
occurs..
Thanks,
Stephen
