Maybe I’m missing something but I f it’s not atomic, it doesn’t matter whether there’s a replica or not: sidekiq (whatever that is) might do a read in-between step 2 and 3.

I see several problems in their setup really

- lack of strong consistency

- using eventually consistent data, the replica, to take business decision

- no concurrency control (pessimistic or optimistic)

I don’t know much about mastodon but, while not trivial, that’s pretty basic systems design concepts