public static MapWork getMapWork(Configuration conf) {
    if (!conf.getBoolean(HAS_MAP_WORK, false)) {
      return null;
    }
    return (MapWork) getBaseWork(conf, MAP_PLAN_NAME);
  }
ReduceField:
KEY: record key
VALUE: record value
ql/src/java/org/apache/hadoop/hive/ql/exec/Utilities.java