Persistent bucket notifications are a very useful and powerful feature. To learn more about it, you can look at this tech talk and usecase example.
Persistent notifications are usually better that synchronous notification, due to several reasons:
- the queue they are using is, in fact, a RADOS object. This gives the queue the reliability level of RADOS
- they do not add the delay of sending the notification to the broker to the client request round trip time
- they allow for temporary disconnects with the broker or broker restarts without affecting the service
- they have a time and attempts retry mechanism