title: MongoDB: MapReduce or Aggregation in a master/slave configuration
body: <p>I am working on the application which understands customer behavior by tracking the user activities using events and pushing them to mongodb.</p>
  
  <p>Now I want to derive the information out of it like % drop at a particular page or the number of users who purchased a product.. so on &amp; so forth.</p>
  
  <p>I went through the topic here on MR vs Aggregation in MongoDB and learnt that MR is not fast enough as compared to aggregation( may be in a non sharded environment). </p>
  
  <ol>
  <li>Is sharded/non sharded setup of mnogo the only reason for choosing MR vs aggregation or vice versa?</li>
  <li>Is MR the strong contender in the situation mentioned above?</li>
  </ol>