title: How does Facebook do it?
body: <p>Have you ever noticed how facebook says “3 friends and 33 others liked this”? I was wondering what the best approach to do this is. I don’t think going through the friends list, and the list of users who “liked this” and comparing them is efficient at all! Do they keep a track of this in the database? That will make the database size very huge. 
  What do you guys think?</p>
  
  <p>Thanks! </p>