title: redis updating a key with the same value and ttl
body: <p>Does redis update the key value and ttl if I set the <strong>same</strong> key value and ttl again before the current ttl expires? When I do so, it doesn't seem to do anything, and the keys expire after the previous set timeout. 
  The code is pretty simple - write the same keys in redis over and over again with the same value and same ttl - but looks like I should be getting the key and setting the new ttl value instead. Is this the case?</p>