Other use cases

Other use cases

Yep - you want to base the notifications on what's interesting to the application, not on the current layering; one for "other readers will see the write" (obvious), one for "this system can crash without losing data, but if the storage stack crashes, you may lose data" (there are commit protocols where this is the point at which you can tentatively acknowledge the write), and one for "data should not be lost even if everything crashes" (since this is the final state for all writes) are still probably the interesting three, no matter how complicated you make the underlying layers.

I can also see some room for splitting the first into two: "other readers on this system" and "other readers with access to this storage stack" - but again, the point has to be "what is interesting to the application about this state", as opposed to "what states do I know about?", with "what states do I know about?" only being useful for preventing you offering notifications you can't provide at a sensible cost.