Receipt Sequence Numbers
Receipt sequence numbers can be used to prevent the Broker from presenting duplicate events to your application's BrokerClient when it retrieves the next event. The Broker always sets sequence numbers on the events it presents to receiving clients. If your receiving client acknowledges an event's sequence number, the Broker will not present that event again.
Note:
Volatile events are not assigned sequence numbers by the Broker, so they cannot be specifically acknowledged. Volatile events are deleted from the client's event queue as soon as they are retrieved by a Broker client.