public String getSessionId() {
    return sessionId;
  }
Close a tez session. Will cleanup any tez/am related resources. After closing a session no
further DAGs can be executed against it. Only called by session management classes; some
sessions should not simply be closed by users - e.g. pool sessions need to be restarted.

@param keepDagFilesDir
         whether or not to remove the scratch dir at the same time.
@throws Exception
ql/src/java/org/apache/hadoop/hive/ql/exec/tez/TezSessionState.java