title: Array lookup speed in PHP; long cache keys
body: <p>I'm working on a method that, due to the expense of it's operation and frequency which it is called with identical arguments, would benefit from caching the return values.</p>
  
  <p>I'll be <code>serialize()</code>-ing the arguments together for cache keys, but this can result in very long keys, due to the lengthy array arguments.</p>
  
  <ul>
  <li>Does PHP array indexing and look-up suffer from such long keys (<em>think from 250B to 1kB+</em>)?</li>
  <li>So far so good, but am I facing a situation where this could fail spectacularly on me at some point?</li>
  <li>Basically, should I <code>md5()</code> (<em>or alternative</em>) the keys?</li>
  </ul>
  
  <hr>
  
  <p><em>Minor clarifications</em>:<br>
  This is only per-request caching, with no permanent storage. The method in question is that of a view helper, and for each view generation it may be called 500 times or more.</p>