presto-orc/src/main/java/io/prestosql/orc/writer/DecimalColumnWriter.java/DecimalColumnWriter/finishRowGroup
class DecimalColumnWriter:    @Override
    public Map<OrcColumnId, ColumnStatistics> finishRowGroup()
    {
        checkState(!closed);
        ColumnStatistics statistics;
        if (type.isShort()) {
            statistics = shortDecimalStatisticsBuilder.buildColumnStatistics();
            shortDecimalStatisticsBuilder = new ShortDecimalStatisticsBuilder(type.getScale());
        }
        else {
            statistics = longDecimalStatisticsBuilder.buildColumnStatistics();
            longDecimalStatisticsBuilder = new LongDecimalStatisticsBuilder();
        }
        rowGroupColumnStatistics.add(statistics);

        return ImmutableMap.of(columnId, statistics);
    }