title: Mongo count really slow when there are millions of records
body: <pre><code>//FAST
  db.datasources.find().count()
  12036788
  
  //SLOW    
  db.datasources.find({nid:19882}).count()
  10161684
  </code></pre>
  
  <p>Index on nid</p>
  
  <p>Any way to make the second query faster? (It is taking about 8 seconds)</p>