presto-hive/src/main/java/io/prestosql/plugin/hive/HivePageSourceProvider.java/HivePageSourceProvider/getIndex
class HivePageSourceProvider:        public int getIndex()
        {
            checkState(kind == ColumnMappingKind.REGULAR || kind == ColumnMappingKind.INTERIM);
            return index.getAsInt();
        }