title: Removing TTL expired keys in Flink Mapstate
body: <p>I need the ability to remove old keys from map state which are older than a fixed amount of time.
  I currently keep the timestamps of each event in the the key state map, and I'd like to have an ansyncronous process which will remove these stale keys.</p>
  
  <p>I'm using RocksDB as state backend, and I don't think that the Java API of RocksDB supports the open with TTL as noted <a href="https://github.com/facebook/rocksdb/wiki/Time-to-Live" rel="nofollow noreferrer">here</a>.</p>
  
  <p>So my questions are:</p>
  
  <ul>
  <li>Is it at all possible to have an async thread that has access to the Mapstate since it runs in an operator function?</li>
  <li>Is there a better practice in this case?</li>
  </ul>
  
  <p>Thanks in advance,</p>