This month’s Maatkit release, which just hit the download servers, contains a new feature for mk-query-digest: Apdex scores. The Apdex performance index is a sensible metric of how satisfactory the response time to a request is. Of all the scientific metrics I’ve seen, it’s the most practical; and of all the practical ones I’ve seen, it’s the most scientific.
To use this feature, you need to know what the Apdex threshold means, and you need to know how to configure this in mk-query-digest.
And then you can ask and answer practical questions such as “which classes of queries against this MySQL server are not satisfying users?” Or, because mk-query-digest supports the HTTP protocol, you can pose the same question about your web application overall.