title: Evaluating mongo DB performance
body: <p>I have a collection in a mongoDB on which I have set user preferences. I  have a very large number of objects in one particular collection, and user can follow a key in the collection. For example:</p>
  
  <pre><code>colletionx { key1: value1, key2: value2 : key3: value3 .. keyn:valuen}
  </code></pre>
  
  <p>Now the user can follow any number of keys, i.e., when key1 equals some value update me. (Very much similar similar to the Twitter "follow" feature).</p>
  
  <p>Now how can I efficiently do this? </p>
  
  <p>Also if I query mongo with a query like this:</p>
  
  <pre><code> db.collection.find({ keyId : 290})
  </code></pre>
  
  <p>or  <code>db.collection.find({ keyId : { $in [ 290] } })</code> will there be any drastic performance improvement when there are millions of users and all follow 1 show.</p>