title: Why is hadoop slow for a simple hello world job
body: <p>I am following the tutorial on the hadoop website: <a href="https://hadoop.apache.org/docs/r3.1.2/hadoop-project-dist/hadoop-common/SingleCluster.html" rel="nofollow noreferrer">https://hadoop.apache.org/docs/r3.1.2/hadoop-project-dist/hadoop-common/SingleCluster.html</a>.
  I run the following example in Pseudo-Distributed Mode.</p>
  
  <pre><code>time hadoop jar hadoop/share/hadoop/mapreduce/hadoop-mapreduce-examples-3.1.2.jar grep input output 'dfs[a-z.]+'
  </code></pre>
  
  <p>It takes 1:47min to complete. When I turn off the network (wifi), it finishes in approx 50 seconds.  </p>
  
  <p>When I run the same command using the Local (Standalone) Mode, it finishes in approx 5 seconds (on a mac). </p>
  
  <p>I understand that in Pseudo-Distributed Mode there is more overhead involved and hence it will take more time, but in this case it takes way more time. The CPU is completely idle during the run.</p>
  
  <p>Do you have any idea what can cause this issue?</p>