title: mongodb as round-robin-database
body: <p>I am using mongo-db for realtime analytics, I am getting 5 million
  data points per day which will increase in future to 10 million at
  least. </p>
  
  <p>my question is:</p>
  
  <p>Capped collections are circular so my data will be overwritten after
  it reaches to the cap and i don't want to loose this data.</p>
  
  <p>So what approach I should follow to keep old data and avoid that this data being overwritten but still being able to use capped since they are fast? </p>
  
  <p>i was thinking in an algorithm like:</p>
  
  <ul>
  <li>rename current collection to old and drop current.</li>
  <li>append old to a search-friendly (not capped) collection</li>
  </ul>