title: Dataflow job drain does not end for a long time
body: <p>Draining of Dataflow streaming job does not end while 1 days.</p>
  <p>No error log on stack driver also.</p>
  <p>job ID is</p>
  <blockquote>
  <p>2018-03-09_00_40_49-15224076611250277770</p>
  <p>2018-02-12_22_35_23-4736481063361562693</p>
  </blockquote>
  <p>What's the problem?</p>
  <p>And, How can I know when this drainig job complete? (predict time)</p>