presto-main/src/main/java/io/prestosql/execution/resourcegroups/StochasticPriorityQueue.java/StochasticPriorityQueue/iterator
class StochasticPriorityQueue:    @Override
    public Iterator<E> iterator()
    {
        // Since poll() is not deterministic ordering is not required
        return index.keySet().iterator();
    }