title: How does spark choose nodes to run executors?(spark on yarn)
body: <p><strong>How does spark choose nodes to run executors?(spark on yarn)</strong>
  We use spark on yarn mode, with a cluster of 120 nodes.
  Yesterday one spark job create 200 executors, while 11 executors on node1, 
  10 executors on node2, and other executors distributed equally on the other nodes.</p>
  
  <p>Since there are so many executors on node1 and node2, the job run slowly.</p>
  
  <p>How does spark select the node to run executors? 
  according to yarn resourceManager?</p>