title: CMS garbage collector - when does it run?
body: <p>I am confused about two parameters that may control when the CMS collector kicks in:</p>
  
  <p><code>MaxHeapFreeRatio</code> (70% by default)</p>
  
  <p><code>CMSInitiatingOccupancyFraction</code> (over 90% by default)</p>
  
  <p>What does each of those parameters mean, exactly? When does the collector start (the marking phase), and collect (the sweeping phase)?</p>