@Explain(displayName = "Execution mode", explainLevels = { Level.USER, Level.DEFAULT, Level.EXTENDED },
      vectorization = Vectorization.SUMMARY_PATH)
  public String getExecutionMode() {
    if (vectorMode &&
        !(getIsTestForcedVectorizationEnable() &&
          getIsTestVectorizationSuppressExplainExecutionMode())) {
      if (llapMode) {
        if (uberMode) {
          return "vectorized, uber";
        } else {
          return "vectorized, llap";
        }
      } else {
        return "vectorized";
      }
    } else if (llapMode) {
      return uberMode? "uber" : "llap";
    }
    return null;
  }
If the plan has a reducer and correspondingly a reduce-sink, then store the TableDesc pointing
to keySerializeInfo of the ReduceSink

@param keyDesc
ql/src/java/org/apache/hadoop/hive/ql/plan/ReduceWork.java