private PrimitiveType getElementType(Type type) {
    if (type.isPrimitive()) {
      return type.asPrimitiveType();
    }
    if (type.asGroupType().getFields().size() > 1) {
      throw new RuntimeException(
          "Current Parquet Vectorization reader doesn't support nested type");
    }

    Type childType = type.asGroupType().getFields().get(0);

    // Parquet file generated using thrift may have child type as PrimitiveType
    if (childType.isPrimitive()) {
      return childType.asPrimitiveType();
    } else {
      return childType.asGroupType().getFields().get(0).asPrimitiveType();
    }
  }
Advances to the next batch of rows. Returns false if there are no more.
ql/src/java/org/apache/hadoop/hive/ql/io/parquet/vector/VectorizedParquetRecordReader.java