title: Measure Rails performance locally like New Relic but without external dependencies
body: <p>Having used New Relic before, I know it can measure performance but it's an external dependency. Now my app contains some faker gem data I noticed some slower performance (loading 1000 user profiles wih attached images).</p>
  
  <ul>
  <li>Are there any tools/gems to measure performance of a Rails app since this is of course important?</li>
  <li>Are there some docs or general guidance on performance and Rails? I know I can use indexes on tables but if you have large app with thousands of users there must be more you can do to improve performance.</li>
  </ul>
  
  <p>Any suggestions on this topic are welcome. The main question would be: are there local New Relic-like gems to measure an app's performance so you can make improvements?</p>