Only one executor is running in spark. only master is working but no one
<p><strong>As i have 10 nodes in cluster, each node consists of 2 cores, altogether there are 20 cores with me. I have set num-executors = 20. But only one master computer is working now. where are other 18 cores ?</strong> </p>

<p><em>Below are the list images showing the UI view of 
performance:</em> </p>

<p><a href="https://i.stack.imgur.com/ws9xR.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/ws9xR.png" alt="enter image description here"></a></p>

<p><a href="https://i.stack.imgur.com/A9qzu.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/A9qzu.png" alt="enter image description here"></a></p>

<p><a href="https://i.stack.imgur.com/xenYk.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/xenYk.png" alt="enter image description here"></a></p>

<p>I have the spark-submit code as below :</p>

<pre><code>./bin/spark-submit --class Package.Class --master spark://master-url:7077 --deploy-mode client --num-executors 20  /home/ec2-user/AWS.jar
</code></pre>

<p><strong>what can i do to improve the performance so that every computer will together and it will have required number of stages or jobs ?</strong></p>