@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;
  }
For each map side operator - stores the alias the operator is working on
behalf of in the operator runtime state. This is used by reduce sink
operator - but could be useful for debugging as well.
ql/src/java/org/apache/hadoop/hive/ql/plan/MapWork.java