Quite a few of these issues too strike me as Celery problems rather than RabbitMQ. I’ve run into many of these similar issues and in every case it was due to Celery’s implementation not using RabbitMQ properly and was fixed with an internal patch to Celery.

The most blatant example is the countdown tasks. Celery has a very strange implementation of these (meant to be broker agnostic) where it consumes the task from queue, sees in the task custom headers (which is meaningless to RabbitMQ) that it should be delayed and then sits on the task and takes a new task. That results in heavy memory load on your celery client holding all these tasks in memory, and if you have acks_late set, RabbitMQ will be sitting on many tasks that are claimed by a client but not acked and _also_ have to sit in memory. But that is 100% a celery problem, not Rabbit, and we solved it by overriding countdowns to use DLX queues instead so that we could use Rabbit-native features. Not surprisingly, Rabbit performs a lot better when you’re using native built-in features.