title: Akka - messages queued up, not being consumed very often
body: <p>I have an Akka based application that performs a large amount of work and reports progress by message passing. The "workers" report when they complete some work up to their "manager" who then feeds them more work and at the same time the "manager" sends a message (fire and forget) to an actor ref which simply keeps track of progress.</p>
  
  <p>The "manager" and "workers" all share a dispatch thread pool, and the "tracker" actor sits in it's own small thread pool. I also throttle how much stuff gets posted to it using a basic modulo of the progress, so i only send a message when 20 items of work are completed each time. This seems to work ok for small numbers of jobs - say a couple of hundred. I see the tracker actor receiving the messages and updating its instance variable and responding to requests to retrieve the progress data.</p>
  
  <p>However, when handling thousands of items of work, the progress count goes up for a little while and then appears to totally stop - as if no messages are being picked up by the tracker actor and they are all just filling up it's message queue. Is the "worker" dispatcher hogging all the resources perhaps? I thought that each dispatcher was supposed to be able to deliver messages to actors with some regularity. I've tried messing about with the "fairness" configuration in each dispatcher but it seems to make no difference.</p>
  
  <p>I value anyone's thoughts on this. </p>