presto-main/src/main/java/io/prestosql/operator/MergeHashSort.java/MergeHashSort/merge
class MergeHashSort:    public WorkProcessor<Page> merge(List<Type> keyTypes, List<Type> allTypes, List<WorkProcessor<Page>> channels, DriverYieldSignal driverYieldSignal)
    {
        InterpretedHashGenerator hashGenerator = createHashGenerator(keyTypes);
        return mergeSortedPages(
                channels,
                createHashPageWithPositionComparator(hashGenerator),
                IntStream.range(0, allTypes.size()).boxed().collect(toImmutableList()),
                allTypes,
                keepSameHashValuesWithinSinglePage(hashGenerator),
                true,
                memoryContext,
                driverYieldSignal);
    }