title: What is the purpose of the instrumentation API in Ruby/Rails?
body: <p>Based on: <a href="http://api.rubyonrails.org/classes/ActiveSupport/Notifications.html" rel="noreferrer">http://api.rubyonrails.org/classes/ActiveSupport/Notifications.html</a></p>
  
  <p>It says: </p>
  
  <blockquote>
    <p>Notifications provides an instrumentation API for Ruby. To instrument an action in Ruby you just need to do:</p>
  </blockquote>
  
  <p>What exactly is an instrumentation API and what does it do?</p>
  
  <h2>Thanks!</h2>