When you start the webapp, the min processes are started. As traffic increases, so does the chance that all processes in the min pool will be busy when a call is made - that will trigger an additional process to start (up to the max setting). The additional process(es) will remain in the pool until the next sweep (which I believe happens every couple of minutes) and, if all processes are still active they remain, and if not, some will be terminated until the process pool is back to the min. The processes that get terminated are whichever ones happen to be idle during the sweep - so you can't count on the up time for any given process to be indicative of a problem (or lack of one). There are rare cases where the min and max pool are set the same and then all processes should have similar up times.