title: Logstash - Trying to create an elapsed filter
body: <p>I'm trying to create an elapsed filter but the elapsed fields don't appear.
  This is the input:</p>
  
  <pre><code>statement =&gt; "SELECT TRANSACTION_ID, COMMUNICATION_ID, 
      BROKER_NAME, IS_NAME, SERVICE_NAME, OPERATION_NAME, OPERATION_VERSION, MESSAGE_TYPE, APPROACH, CLIENT_ID, 
      APPLICATION_ID, EXT_SESSION_ID, EXT_TRANSACTION_ID, EXT_ORIGIN, LANG_CODE, EXT_HOST, APPLICATION, CHANNEL, 
      NUM_RETRIES, STATUS_CODE, STATUS_MSG, DATE_CREATED, 
      DESTINATION_HOST, OPERATION_ID 
      FROM IIB_OPER.COMMUNICATION_LOG 
      WHERE DATE_CREATED &gt; '2018-07-20'"
  </code></pre>
  
  <p>And this is the filter:</p>
  
  <pre><code>filter {
      if [message_type] == "Req" {
          mutate {
              add_tag =&gt; [ "taskStarted" ]
          }
      }
      if [message_type] == "Res" {
          mutate {
              add_tag =&gt; [ "taskTerminated" ]
          }
      }   
      elapsed {
          unique_id_field =&gt; "operation_id"
          start_tag =&gt; "taskStarted"
          end_tag =&gt; "taskTerminated"
          timeout =&gt; 20000
          new_event_on_match =&gt; true
      }
  }
  </code></pre>
  
  <p>In Kibana, in the index patterns, the fields appear but when i get the logstash to work the elapsed fields don't appear.</p>
  
  <p>Any idea why?</p>
  
  <p>Cheers, </p>