How is consumer_capacity computed

[Gaël LE BELLEGO]

Hello all.

We have set up a spring integration bridge (using spring channel adapters and com.rabbitmq.* factories and classes).

The message pipeline works well, but we see odd metrics from rabbitMq console.. especially we noticed that the "consumer_capacity" starts at 100% when there is no consumer,  caps to "98%" when there is a consumer but not messages and eventually collapses to 0% when we add a consumer (and input messages indeed).
No matter the amount of messages sent, the consumer_capacity remains stuck to the floor!

We thus try to understand the matter.

But we are first puzzled about "consumer capacity" definition (https://www.rabbitmq.com/consumers.html#metrics-capacity). It states it is a fraction of "the time", but it seems to us a fraction should be between two things: the time and .. stg else. And we cannot understand what is that second part in the definition.
We tried to have a look at source code, but we must confess we are not familiar with erlang (and provided it is actually the piece of code that feeds the GUI metric).
https://github.com/rabbitmq/rabbitmq-server/blob/master/deps/rabbit/src/rabbit_queue_consumers.erl#L575


We are thus trying to understand how this metric is computed!
If someone could help clarify this a little, it would help us a lot!

And if you happen to have any idea about why this capacity is 0% here, any hint is welcome!