title: Improve Rails loading time
body: <p>This is a bit of a follow-up from <a href="https://stackoverflow.com/q/4736546/305019">a previous question on improving rails console loading time</a>.</p>
  <p>The first great suggestion was to figure out <a href="https://stackoverflow.com/a/5071198/305019">which gems take too long</a>.</p>
  <p>Next answer, suggested using <code>:require =&gt; nil</code> and <a href="https://stackoverflow.com/a/7146810/305019">loading those gems later</a>.</p>
  <p>With some gems however, it's not entirely clear how to accomplish this without breaking things. Here's a list of our 'biggest offenders', I wonder if someone can suggest the best approach to loading them only when necessary?</p>
  <pre><code>require gon: 2.730000 (2.870059)
  require omniauth-openid: 1.410000 (1.503858)
  require cancan: 2.640000 (2.707467)
  require fog: 2.730000 (2.846530)
  require activeadmin: 3.650000 (3.923877)
  </code></pre>
  <p>and of course there are many more that take around 1 second or less, which also adds up... but at least removing the big ones will already improve things.</p>
  <h3>how can I selectively load gems later to make rails load faster?</h3>