RabbitMQ - figuring out how many more consumers you can add to a queue

Using the field Consumer utilisation in the RabbitMQ interface can get you a figure of how many more consumers you can add to a queue. Often developers find themselves wondering how well they can scale their applications. Consumer utilisation is a great measure for this and can be found when you look at a queue in the web interface:

Consumer utilisation

Above I currently have zero consumers or no messages. Therefore the utilisation is 0. If rabbit could not keep up and I had too many consumers, then this would have been at 100%. Often you will see this being much lower and RabbitMQ can keep up. So if your utilisation is at 10% with one consumer. Then you should be able to add about ten more consumers. Other than adding more consumers to a queue you can also change the prefetch count for your consumers. This will make them prefetch more and acknowledge the messages as they are handling them.