@Explain(vectorization = Vectorization.SUMMARY, displayName = "Map Vectorization", explainLevels = { Level.DEFAULT, Level.EXTENDED })
  public MapExplainVectorization getMapExplainVectorization() {
    if (!getVectorizationExamined()) {
      return null;
    }
    return new MapExplainVectorization(this);
  }
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