[n42]

I think he's talking about how with FoundationDB, pub/sub notifications ("watches") are transactional – the notification is only sent if the transaction succeeds. because FoundationDB can guarantee transactions across multiple key writes, you can write your state at the same time you write an event/message/job somewhere else, in one transaction, with the subscriber only being notified on success. I think this is impossible(?) to achieve without the message queue and data store being the same service.

otherwise, you have a transaction to write to your database and a separate call to the message queue, which introduces the race condition.

https://apple.github.io/foundationdb/features.html#watches