minthreads is the starting number of available worker threads eg a setting of 20 will allow at least 20 concurrent booster threads to handle requests.
maxthreads is the maximum number of worker threads booster will allow. eg a setting of 100 will allow a maximum of 100 concurrent requests to be processed by booster.
portbacklog is the ip queuing mechanism, a value of 20 will allow up to 20 ip connections to be queued (waiting for booster thread to become available to service them). Typically this will only be used when more than the maxthreads number of connections make simultaneous requests.