public boolean isSeenOp(Task task, Operator operator) {
    List<Operator<?extends OperatorDesc>> seenOps = taskToSeenOps.get(task);
    return seenOps != null && seenOps.contains(operator);
  }
@param opTaskMap
         reducer to task mapping
ql/src/java/org/apache/hadoop/hive/ql/optimizer/GenMRProcContext.java