title: database implementation for apps like instagram
body: <p>I'm wondering how do apps like snapchat and instagram store pictures and user records in database. </p>
  
  <p>Say I have a user table, how would they maintain list of followers for each user? Would they store the list of followers for each entry in user table or make a separate table for follow event and make an entry every time someone follows someone.</p>
  
  <p>Also, for storing pictures, I'm guessing they would dump the pictures in a mass storage server space and store the URL in tables. Is there a better way of implementing this? If not, what kind of mass storage server would they go for? Dedicated or shared servers?</p>
  
  <p>Thanks.</p>