title: Mongodb compare two big data collection
body: <p>I want to compare two very big collection, the main of the operation is two know what element is change or deleted
  My collection 1 and 2 have a same structure and have more 3 million records
  example :
  record 1 <code>{id:'7865456465465',name:'tototo', info:'tototo'}</code></p>
  
  <p>So i want to know : what element is change, and what element is not present in collection 2.
  What is the best solution to do this?</p>