presto-main/src/main/java/io/prestosql/operator/StatisticsWriterOperator.java/StatisticsWriterOperator/getRowCount
class StatisticsWriterOperator:    private static long getRowCount(Collection<ComputedStatistics> computedStatistics)
    {
        return computedStatistics.stream()
                .map(statistics -> statistics.getTableStatistics().get(ROW_COUNT))
                .filter(Objects::nonNull)
                .mapToLong(block -> BIGINT.getLong(block, 0))
                .reduce((first, second) -> first + second)
                .orElse(0L);
    }