title: Reuse of a Stream is a copy of stream or not
body: <p>For example, there is a keyed stream:</p>
  
  <pre><code>val keyedStream: KeyedStream[event, Key] = env
      .addSource(...)
      .keyBy(...)
  
  // several transformations on the same stream
  keyedStream.map(....)
  keyedStream.window(....)
  keyedStream.split(....)
  keyedStream...(....)
  </code></pre>
  
  <p>I think this is the reuse of same stream in Flink, what I found is that when I reused it, the content of stream is not affected by the other transformation, so I think it is a copy of a same stream.</p>
  
  <ul>
  <li><p>But I don't know if it is right or not.</p></li>
  <li><p>If yes, this will use a lot of resources(which resources?) to keep the copies ?</p></li>
  </ul>