presto-main/src/main/java/io/prestosql/operator/DistinctLimitOperator.java/DistinctLimitOperator/addInput
class DistinctLimitOperator:    @Override
    public void addInput(Page page)
    {
        checkState(needsInput());

        inputPage = page;
        unfinishedWork = groupByHash.getGroupIds(page);
        processUnfinishedWork();
        updateMemoryReservation();
    }