As I mentioned the code that writes the event to the db notifies the client about it, so it knows about the client. This isn't really an issue.

In the case of an exchange I never split a single order book across multiple servers, but I can imagine a lot of applications where this could be an issue. How do you handle data consistency across nodes? Ultimately you have to solve the same issue...

Again, this isn't a big limitation for my use case. That said your answer has certainly given me a greater understanding of other circumstances where it would be very useful. Thank you.