title: Google AppEngine: What is SystemServiceServlet and its relation to the _ah directory?
body: <p>Similar to <a href="https://stackoverflow.com/questions/12796589/how-to-disable-systemserviceservlet-configuration-in-app-engine-project">this</a> question, I'm interested in what this <code>SystemServiceServlet</code> even is, and what it's relationship is to the <code>/_ah/spi/</code> directory I see in the autogenerated web.xml.</p>
  
  <p>What purpose do these serve? Why/when are the necessary? Thanks in advance!</p>