title: concurrency in delayed_jobs
body: <p>I have ROR application and 1 delay_job process ran using rake job:work.
  ROR application add Job in multiple queue.</p>
  
  <p>Lets say we have queue 1 and queue 2.<br>
  My Question is task in queue 1 and task in queue 2 will be executed concurrently? </p>
  
  <p>Currently in my application after running rake job:work process only 1 thread is spawn which executes queue1 task and then queue2 task.<br>
  If i have to execute in parallel, i have to run two rake task of job:work.</p>
  
  <p>Is it correct behavior or it can be run concurrently in 1 rake task of job:work.
  And what is worker in Delay Job. Is delay Job interchangeably used with worker</p>
  
  <p>Thanks<br>
  Priyanka</p>