title: Should I go with MySql or mongodb
body: <p>I am building a social network (connections and their connections, messages and locations) and I am a little confused in deciding whether to go with a relational database (MySQL) or a no-sql system (MongoDB) when designing our backend APIs. Does anyone have any views on what to use when?</p>
  
  <p>PS: I am building developer APIs for developers to tap into our system with oAuth. So scalability and performance is also key factor. Rails 3 + Devise (most likely).</p>