title: What database do online games like Farmville use?
body: <p>Apart from graphical features, online games should have a simple Relational Database structure. I am curious what database do online games like <code>Farmville</code> and <code>MafiaWars</code> use?</p>
  
  <p>Is it practical to use SQL based databases for such programs with such frequent writes ?<br>
  If not, how could one store the relational dependence of users in these games?</p>
  
  <p><strong>EDIT:</strong> As pointed, they use NOSQL databases like <code>Couchbase</code>. NOSQL is fast with good cuncurrency (which is really needed here); but the sotrage size is much larger (due to key/value structure). 
  1. Does't it slow down the system (as we need to read large database files from the disk)? 
  2. We will be very limited as we do not have SQL's <code>JOIN</code> to connected different sets of data.</p>