title: Dataflow: system lag keeps going up
body: <p>We are testing Cloud Dataflow which pulls message from Pub/Sub subscription and convert data to BigQuery TableRow and load them to BigQuery as load job in every 1 min 30 sec.</p>
  
  <p>We can see the pipeline works well and can process 500,000 elements per second with 40 workers. But when trying autoscaling, the number of workers unexpectedly goes up to 40 and stay there even if we send only 50,000 messages to Pub/Sub. In this situation, no unacknowledged message and workers' CPU utilizations are bellow 60%. One thing we noticed is that the Dataflow system lag goes up slowly.</p>
  
  <ol>
  <li>Is system lag affects autoscaling?</li>
  <li>If so, is there any solutions or ways to debugging this problem?</li>
  </ol>