title: Why Spark stage's Executor Computing Time takes much more time than usual when run as the first action?
body: <p>Here's my code:</p>
  
  <pre><code>import time
  import random
  
  NUM_SAMPLES = 1000000
  def sample(p):
    x, y = random.random(), random.random()
    return 1 if x*x + y*y &lt; 1 else 0
  
    count = sc.parallelize(xrange(0, NUM_SAMPLES)).map(sample).reduce(lambda a, b: a + b)
  print "Pi is roughly %f" % (4.0 * count / NUM_SAMPLES)
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/3aDty.png" alt="enter image description here"></p>
  
  <p>Here's the stages page, it takes about 0.5s much more time for the stage0 than the other stages and I want to know where the 0.5s gone? Additional info, the main different is in Executor Computing Time.</p>
  
  <p><img src="https://i.stack.imgur.com/6w5pK.png" alt="enter image description here"></p>