public boolean hasReplicationState() {
    return replicationState != null;
  }
this method is used to identify all the tasks in a graph.
the graph however might get created in a disjoint fashion, in which case we can just update
the number of tasks using the "update" method.
ql/src/java/org/apache/hadoop/hive/ql/exec/repl/util/TaskTracker.java