title: How to restart DAG in Airflow?
body: <p>One of my DAGs with many steps stopped part way through because of a DB shutdown. I'd like to get the DAG to start where it left off but all I can do is start the individual tasks of the DAG one by one. Is there a way to tell Airflow to start the DAG where it left off based on the success of the tasks already completed?</p>
  
  <p>Here's a sample where one of the first tasks finished and the rest are queued or have no status:
  <a href="https://i.stack.imgur.com/F6KDT.png" rel="noreferrer"><img src="https://i.stack.imgur.com/F6KDT.png" alt="enter image description here"></a></p>
  
  <p>When I click on an individual task (<code>runme_1</code>) I can restart it:
  <a href="https://i.stack.imgur.com/GoeR1.png" rel="noreferrer"><img src="https://i.stack.imgur.com/GoeR1.png" alt="enter image description here"></a></p>
  
  <p>However, if I try to start a task which hasn't had it dependencies met (such as <code>run_after_loop</code>), I see the following error message:
  <a href="https://i.stack.imgur.com/dRi7b.png" rel="noreferrer"><img src="https://i.stack.imgur.com/dRi7b.png" alt="enter image description here"></a></p>
  
  <p>I'd like to be able to click on any task, ask it to be queued and have all dependencies run in the correct order. Is that possible?</p>
  
  <p>I'm running Airflow 1.9.0.</p>