title: Get random / any value from Redis hash
body: <p>I have a Redis-Hash with millions of elements, constantly adding new ones. 
  In php, I run an endless loop to get, process, and delete one element afteh the other.
  Hereby, I need to get the key of any existing element (preferebly the first one inserted in the hash, FiFo)</p>
  
  <pre><code>while($redis-&gt;hlen()) {
      $key = ???
      // process $key    
  }
  </code></pre>
  
  <p>While I know the <code>RANDOMKEY</code> and the <code>SRANDMEMBER</code> command, I did not find any way to get a key of a hash. <code>HGETALL</code> and <code>HKEYS</code>are, due to the size of the hash, not an option either. I need sequential processing.
  Help appreciated.</p>