The challenge is that the... «Designing Data-Intensive Applications: The Big Ideas Behind Reliable, Scalable, and Maintainable Systems»

The challenge is that the assumption of stateless clients and request/response interactions is very deeply ingrained in our databases, libraries, frameworks, and protocols. Many datastores support read and write operations where a request returns one response, but much fewer provide an ability to subscribe to changes—i.e., a request that returns a stream of responses over time.

In order to extend the write path all the way to the end user, we would need to fundamentally rethink the way we build many of these systems: moving away from request/response interaction and toward publish/subscribe dataflow. I think that the advantages of more responsive user interfaces and better offline support would make it worth the effort. If you are designing data systems, I hope that you will keep in mind the option of subscribing to changes, not just querying the current state.