title: Submiting the same oozie workflow job multiple times at the same time
body: <p>I am wondered how oozie handle conflicts(if there really exists) when I submit two same workflow job(just the Oozie sample examples) at the same time.
  I can submit the same two job successful and oozie server return two different jobId.In Oozie Web Console, I saw status of two job are all RUNNING, then all SUCCEEDED after some time.
  My workflow.xml as followers:</p>
  
  <pre><code>&lt;workflow-app xmlns="uri:oozie:workflow:0.2" name="map-reduce-wf"&gt;
      &lt;start to="mr-node"/&gt;
      &lt;action name="mr-node"&gt;
          &lt;map-reduce&gt;
              &lt;job-tracker&gt;${jobTracker}&lt;/job-tracker&gt;
              &lt;name-node&gt;${nameNode}&lt;/name-node&gt;
              &lt;prepare&gt;
                  &lt;delete path="${nameNode}/user/${wf:user()}/mapreduce_test/output-data"/&gt;
              &lt;/prepare&gt;
              &lt;configuration&gt;
                  &lt;property&gt;
                      &lt;name&gt;mapred.job.queue.name&lt;/name&gt;
                      &lt;value&gt;default&lt;/value&gt;
                  &lt;/property&gt;
                  &lt;property&gt;
                      &lt;name&gt;mapred.mapper.class&lt;/name&gt;
                      &lt;value&gt;org.apache.oozie.example.SampleMapper&lt;/value&gt;
                  &lt;/property&gt;
                  &lt;property&gt;
                      &lt;name&gt;mapred.reducer.class&lt;/name&gt;
                      &lt;value&gt;org.apache.oozie.example.SampleReducer&lt;/value&gt;
                  &lt;/property&gt;
                  &lt;property&gt;
                      &lt;name&gt;mapred.map.tasks&lt;/name&gt;
                      &lt;value&gt;1&lt;/value&gt;
                  &lt;/property&gt;
                  &lt;property&gt;
                      &lt;name&gt;mapred.input.dir&lt;/name&gt;
                      &lt;value&gt;/user/${wf:user()}/mapreduce_test/input&lt;/value&gt;
                  &lt;/property&gt;
                  &lt;property&gt;
                      &lt;name&gt;mapred.output.dir&lt;/name&gt;
                      &lt;value&gt;/user/${wf:user()}/mapreduce_test/output-data/&lt;/value&gt;
                  &lt;/property&gt;
              &lt;/configuration&gt;
          &lt;/map-reduce&gt;
          &lt;ok to="end"/&gt;
          &lt;error to="fail"/&gt;
      &lt;/action&gt;
      &lt;kill name="fail"&gt;
          &lt;message&gt;Map/Reduce failed, error message[${wf:errorMessage(wf:lastErrorNode())}]&lt;/message&gt;
      &lt;/kill&gt;
      &lt;end name="end"/&gt;
  &lt;/workflow-app&gt;
  </code></pre>
  
  <p>I know in the "prepare" label delete output directory helps make the action repeatable and enables retries after failure, I also understand the basic action run model.</p>
  
  <p>So, My questions are:</p>
  
  <ol>
  <li>The same two jobs are really running concurrently?(I saw the two all in running state in oozie web console). </li>
  <li>Is there exists write conflict?(two same job point one output directory)</li>
  </ol>