@Override
  public Descriptor getDescriptor() {
    VectorExpressionDescriptor.Builder b = new VectorExpressionDescriptor.Builder();
    b.setMode(VectorExpressionDescriptor.Mode.PROJECTION).setNumArguments(2)
        .setInputExpressionTypes(VectorExpressionDescriptor.InputExpressionType.COLUMN,
            VectorExpressionDescriptor.InputExpressionType.COLUMN);

    setArguments(b);
    return b.build();
  }
The actual hash method for an item in the input vectors. This implementation is supposed to be
in line with non-vectorized one (ObjectInspectorUtils.getBucketHashCode) for multiple fields.
The method is abstract and is supposed to be implemented in subclasses.
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/expressions/MurmurHashExpression.java