presto-orc/src/main/java/io/prestosql/orc/OrcWriter.java/OrcWriter/finishRowGroup
class OrcWriter:    private void finishRowGroup()
    {
        Map<OrcColumnId, ColumnStatistics> columnStatistics = new HashMap<>();
        columnWriters.forEach(columnWriter -> columnStatistics.putAll(columnWriter.finishRowGroup()));
        recordValidation(validation -> validation.addRowGroupStatistics(columnStatistics));
        rowGroupRowCount = 0;
    }