title: How to choose from MMAPV1, WiredTiger or In-Memory StorageEngine for MongoDB?
body: <p>In MongoDb Documentation 3.2 I saw that they support 3 Storage Engine,
  MMAPV1, WiredTiger, In-Memory, it is very confusing which one to choose. </p>
  
  <p>I have the sensation from the description that <code>WiredTiger</code> is better than <code>MMAPV1</code>, but in other sources they say that MMAPV1 is better for heavy reads... and WiredTiger for heavy writes... </p>
  
  <p>Is there some constraints when to choose one over the other ?
  Can someone suggest some best practices for example</p>
  
  <p>when I have this type of application usually is best this , else choose an other...</p>