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I have a exchange and only one queue bind to it. When the message publishing rate goes over some cap the rabbitmq automatically throttles the incoming message rate.

On further investigation i found this happens due to the "Flow control" trottling mechanism built in rabbitmq. https://www.rabbitmq.com/blog/2014/04/14/finding-bottlenecks-with-rabbitmq-3-3/

As per this document i have connection, channels in flow control and not the queue. which means there is a cpu-bound / disk-bound limit.

My messages are not persistent so i don't have disk limitation. On Searching, i found documents stating a queue is limited to single cpu. https://groups.google.com/forum/#!msg/rabbitmq-users/wzHMV7F0ugU/zhW_9b8ACQAJ

What does it mean ? do the rabbitmq queue process uses only 1 cpu even multiple cores are available in the machine? what is the limitation of cpu with respect to queue flow control?

Artandor
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A queue is handled by one and one only CPU, which mean that you have to design your message flow through rabbit with multiple queue in order to remain scalable.

If you are on one queue only you will be limited to a maximum number of messages no matter if you have 1 or more cores

https://www.rabbitmq.com/queues.html#runtime-characteristics

If you have a specific need to build an architecture with only one logical queue, which is explicitely not recommended ; or if you have a queue with a really high trafic, you can check sharded queues here : Github Sharded queues Plugin

It's a pluggin (take with caution and test everything before going to production, especialy failure and replication) that split a logical queue name into multiple queues.

If you are running a benchmark on rabbitmq, remember to produce and consume on a number of queues superior to the amount of CPU cores present on the server. Other tips about benchmark, try to produce only, consume only, and both at the same time, with different persistence settings (persistence, message size, lazy queues, ...) and ack settings.

Artandor
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