@Override
  @Explain(displayName = "Map Operator Tree", explainLevels = { Level.USER, Level.DEFAULT, Level.EXTENDED },
      vectorization = Vectorization.OPERATOR_PATH)
  public Set<Operator<? extends OperatorDesc>> getAllRootOperators() {
    Set<Operator<?>> opSet = new LinkedHashSet<Operator<?>>();

    for (Operator<?> op : getAliasToWork().values()) {
      opSet.add(op);
    }
    return opSet;
  }
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