presto-orc/src/main/java/io/prestosql/orc/metadata/OrcMetadataWriter.java/OrcMetadataWriter/toRowGroupIndex
class OrcMetadataWriter:    private static RowIndexEntry toRowGroupIndex(RowGroupIndex rowGroupIndex)
    {
        return OrcProto.RowIndexEntry.newBuilder()
                .addAllPositions(rowGroupIndex.getPositions().stream()
                        .map(Integer::longValue)
                        .collect(toList()))
                .setStatistics(toColumnStatistics(rowGroupIndex.getColumnStatistics()))
                .build();
    }