public String createDagName(Configuration conf, QueryPlan plan) {
    String name = getUserSpecifiedDagName(conf);
    if (name == null) {
      name = plan.getQueryId();
    }

    assert name != null;
    return name;
  }
Singleton
@return instance of this class
ql/src/java/org/apache/hadoop/hive/ql/exec/tez/DagUtils.java