title: How many simultaneous requests can I send to ElasticSearch cluster?
body: <p>I want to send multiple bulk operation requests to ElasticSearch cluster, and I come across this issue <code>EsRejectedExecutionException[rejected execution (queue capacity 50) on org.elasticsearch.action.support.replication.TransportShardReplicationOperationAction</code></p>
  
  <p>I have a cluster of 4 ElasticSearch instances (version 1.3.4), when I sent this request to get the number of its bulk operation thread pool size:</p>
  
  <pre><code>GET /_cat/thread_pool?v&amp;h=host,bulk.active,bulk.queueSize
  </code></pre>
  
  <p>I got </p>
  
  <pre><code>host    bulk.active bulk.queueSize
  1D4HPY1           0             50 
  1D4HPY2           0             50
  1D4HPY3           0             50 
  1D4HPY4           0             50
  </code></pre>
  
  <p>So how many simultaneous bulk operation requests I can send to that cluster? <code>50 or 200</code>?</p>