title: symfony 2.3 clear cache command takes a long time
body: <p>when I remove the cache <strong>it takes too much time</strong> because my cache folders are large.
  folder size in three days :</p>
  
  <pre><code>$ du -sh app/cache/*
  2.6M    app/cache/dev
  46M     app/cache/prod
  363M    app/cache/prod_old
  </code></pre>
  
  <p>how to speed up this process ?</p>