title: How to fix Redis "memory leak"
body: <p>I'm using a redis memory store on dotcloud but despite expiring keys its used_memory never drops back down again.  Using <code>flushdb</code> or <code>flushall</code> from redis-cli doesn't cause the used_memory to drop from it's ~20Mb.  I've had the same problem on RedisToGo.</p>
  
  <p>Anyone know how am I managing to fill it up? and how can I avoid doing this?  Perhaps there are certain characters you shouldn't put into redis values or keys?  I'm using it with EM and resque from a heroku rails app.</p>