presto-main/src/main/java/io/prestosql/sql/planner/planprinter/OperatorInputStats.java/OperatorInputStats/merge
class OperatorInputStats:    public static OperatorInputStats merge(OperatorInputStats first, OperatorInputStats second)
    {
        return new OperatorInputStats(
                first.totalDrivers + second.totalDrivers,
                first.inputPositions + second.inputPositions,
                first.sumSquaredInputPositions + second.sumSquaredInputPositions);
    }