However, it is not possible for queue subscriptions - and they seem to be the most popular subscriptions - since a queue member can receive message sequences completely out of order. For instance, a member could receive message 1 to 10, while another member of the same group receive messages 11, 13 and 15. If the first member exits without acknowledging its messages, messages 1 to 10 may be redelivered to the member that already received messages 11, 13 and 15. So the concept of "floor" would not work. Some map/time-based detection approach could work, but is currently not implemented in any of the supported libraries.