How to Read the haproxy Stats Page

For those of you using HAProxy along with the stats papge (haproxy?stats), how do I interpret this page? There is no decent explanation.

For instance: Which Session column displays the number of currently active connections to the backend? Session or Sessions Rate?

Session rate is the number of new sessions per second. Under sessions, cur is the current number of sessions, max is the maximum concurrent sessions, total is the total number of sessions since haproxy was restarted.

I think what you are confused about is the difference between concurrency and arrival rate.

Concurrency is how many things are going on at a snapshot in time. The Arrival rate is how many new things arrived during a window of time.

For Example:

During the snapshot there were two concurrent events. The arrival rate during that entire second is 5 events, because there were 5 events that started throughout that second. The key relationship to grasp is that a large amount of concurrent connections can come from a high arrival rate and/or long lived connections (see Little's Law).