title: How to control the parallelism or concurrency of an Airflow installation?
body: <p>In some of my Apache Airflow installations, DAGs or tasks that are scheduled to run do not run even when the scheduler doesn't appear to be fully loaded. How can I increase the number of DAGs or tasks that can run concurrently?</p>
  <p>Similarly, if my installation is under high load and I want to limit how quickly my Airflow workers pull queued tasks (such as to reduce resource consumption), what can I adjust to reduce the average load?</p>