title: Datastore vs Cloud SQL in Google App Engine
body: <p>I want to build an application that will serve a lot of people (more than 2 million) so I think that I should use <a href="https://cloud.google.com/datastore/" rel="noreferrer">Google Cloud Datastore</a>. However I also know that there is an option to use <a href="https://cloud.google.com/sql/" rel="noreferrer">Google Cloud SQL</a> and still serve a lot of people using <a href="https://www.mysql.com/" rel="noreferrer">mySQL</a> (like what Facebook and Youtube do).<br><br>
  Is this a correct assumption to use Datastore rather that the relational Cloud SQL with this many users? Thank you in advance </p>