presto-main/src/main/java/io/prestosql/operator/RowNumberOperator.java/RowNumberOperator/addInput
class RowNumberOperator:    @Override
    public void addInput(Page page)
    {
        checkState(!finishing, "Operator is already finishing");
        requireNonNull(page, "page is null");
        checkState(!hasUnfinishedInput());
        inputPage = page;
        if (groupByHash.isPresent()) {
            unfinishedWork = groupByHash.get().getGroupIds(inputPage);
            processUnfinishedWork();
        }
        updateMemoryReservation();
    }