title: python apscheduler - skipped: maximum number of running instances reached
body: <p>I am executing a function every second using Python apscheduler (version 3.0.1)</p>
  
  <p><strong>code</strong>:</p>
  
  <pre><code>scheduler = BackgroundScheduler()
  scheduler.add_job(runsync, 'interval', seconds=1)
  scheduler.start()
  </code></pre>
  
  <p>It's working fine most of the time but sometimes I get this warning:</p>
  
  <pre><code>WARNING:apscheduler.scheduler:Execution of job "runsync (trigger: interval[0:00:01], next run at: 2015-12-01 11:50:42 UTC)" skipped: maximum number of running instances reached (1)
  </code></pre>
  
  <p>1.Is this the correct way to execute this method?</p>
  
  <p>2.What does this warning mean? Does it affect the execution of tasks inside the function in anyway?</p>
  
  <p>3.how to handle this?</p>