private static MapWork populateMapWork(JobConf jobConf, String inputName) {
    MapWork work = null;
    if (inputName != null) {
      work = (MapWork) Utilities.getMergeWork(jobConf, inputName);
      // work can still be null if there is no merge work for this input
    }
    if (work == null) {
      work = Utilities.getMapWork(jobConf);
    }

    return work;
  }
get the size estimates for each bucket in tasks. This is used to make sure
we allocate the head room evenly
ql/src/java/org/apache/hadoop/hive/ql/exec/tez/SplitGrouper.java