The actual mind-blowing scale is that Apple's push notification service isn't just carrying iMessages. It's also carrying push notifications for every third-party messaging app.
And the non-messaging apps with notifications too.
And the silent internal notifications. You added a meeting to your calendar on your Mac? Push notification to your iPhone to tell it that the iCloud data changed and it needs to update. Changed a file on iCloud Drive? Push notification to sync your other devices. Got a phone call, and it starts ringing on your Mac too via Continuity? Push notification (encrypted like an iMessage).
Just how many messages are going through that service every second?!
Centralized notifications is not a "genius solution", it is the "only possible solution" for power-constrained devices, if you think about it. Same thing applies to Android: in ideal world it keeps a single connection open to GCM servers to listen for notifications for ALL apps on the device, and then routes messages to the appropriate applications they are intended for.
I never said centralized notifications is conceptually a genius solution. I said actually building a system that can handle so many billion notifications is impressive. I'm curious how it works internally...
And the non-messaging apps with notifications too.
And the silent internal notifications. You added a meeting to your calendar on your Mac? Push notification to your iPhone to tell it that the iCloud data changed and it needs to update. Changed a file on iCloud Drive? Push notification to sync your other devices. Got a phone call, and it starts ringing on your Mac too via Continuity? Push notification (encrypted like an iMessage).
Just how many messages are going through that service every second?!