public void addSeenOp(Task task, Operator operator) {
    List<Operator<?extends OperatorDesc>> seenOps = taskToSeenOps.get(task);
    if (seenOps == null) {
      taskToSeenOps.put(task, seenOps = new ArrayList<Operator<? extends OperatorDesc>>());
    }
    seenOps.add(operator);
  }
@param opTaskMap
         reducer to task mapping
ql/src/java/org/apache/hadoop/hive/ql/optimizer/GenMRProcContext.java