We don't want several rollback jobs to be running at the same time, so concurrency is 1. We could use [this plugin](https://github.com/brainopia/sidekiq-limit_fetch) to limit worker per queue, but that requires redis 2.6+ and I don't think we are there yet (correct me if that's not the case my VM is not very fresh). At the moment this limit is not a problem as we're running just this single type of jobs.