title: Why Rails change Set-Cookie header every request for the same session
body: <p>I'm using Rails 4 with cookie based session store, found that Rails 4 will give me a different cookie every time I refresh the page, but it can still identify me.</p>
  
  <p>Compare it to another rack app which uses <code>Rack::Session::Cookie</code>, it will only send <code>Set-Cookie</code> for the first request, until some changes to session data were made.</p>
  
  <p>Why are they designed differently? Is there any reason behind?</p>