presto-main/src/main/java/io/prestosql/operator/DistinctLimitOperator.java/DistinctLimitOperator/processUnfinishedWork
class DistinctLimitOperator:    private boolean processUnfinishedWork()
    {
        verifyNotNull(unfinishedWork);
        if (!unfinishedWork.process()) {
            return false;
        }
        groupByIds = unfinishedWork.getResult();
        unfinishedWork = null;
        return true;
    }