title: Spark streaming - waiting for data for window aggregations?
body: <p>I have data in the format { host | metric | value | time-stamp }.  We have hosts all around the world reporting metrics.</p>
  
  <p>I'm a little confused about using window operations (say, 1 hour) to process data like this.</p>
  
  <ul>
  <li><p>Can I tell my window when to start, or does it just start when the application starts?  I want to ensure I'm aggregating all data from hour 11 of the day, for example.  If my window starts at 10:50, I'll just get 10:50-11:50 and miss 10 minutes.</p></li>
  <li><p>Even if the window is perfect, data may arrive late.</p></li>
  </ul>
  
  <p>How do people handle this kind of issue? Do they make windows far bigger than needed and just grab the data they care about on every batch cycle (kind of sliding)?</p>