Hello and thankyou for your question.
Firstly, my apologies for the delay. There is an issue with the Wrox notification system and I was not being notified of new messages.
As for your question. In short yes, there is always the possibility that there could be a failure at any point. By adding a message after each operation, you reduce the potential for a failure to cause harm.
But, there's always that small chance it will happen at an awkward moment. The strategy here is to minimise the possibility as much as possible.
As we talked about in the book, though. If you can make your operations idempotent the problem goes away. If you REALLY REALLY REALLY
cannot tolerate failure, you may want to investigate distributed locking as described by Martin Kleppmann http://martin.kleppmann.com/2016/02/...d-locking.html
Hope that helps and I hope the late response does not cause offence.