I like to say that the philosophy of OpenTSDB is to collect *everything* and later figure out what's actually useful.  Sometimes you don't know that a metric is useful until the time you write a postmortem.  And then you'll be happy to have all the data.

For instance here you're missing several important metrics such as `backend_req`, `backend_busy`, `backend_unhealthy`, `backend_fail`, `accept_fail`, `n_wrk`, `n_wrk_create`, `n_wrk_failed`, etc etc.

Just collect everything, it's cheap.  And on the one day where you need it, it will help you so much that you'll be happy to have collected all this data all along.