Yes, we have natural sharding by user. However Core Data also can create shares which multiple users can access. I don't think this typically causes high concurrency, it's more like a Dropbox file share or a Google docs file share for a few users at a time.

This definitely helped them make the choice to run SQLite on the server.

But I still think it's super cool. We're talking 1.8 billion devices with data stored as SQLite files in the cloud.

I would assume single account but multiple devices, so you could have multiple connections syncing at once.