nathanl
Has anybody used Elixir to check the length of a RabbitMQ queue? It can be done with declare_queue, but it’s ugly - you have to pass the exact option you originally declared the queue with, plus :passive.
The use case is to detect when the system is backing up and respond accordingly.
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collegeimprovements
If you can use
GenRmqthen it has message count, message_count functions.nathanl
@collegeimprovements Oh thanks - that led me to the underlying function: AMQP.Queue — amqp v1.4.2 . Works great!
collegeimprovements
Glad to see this
nathanl
For anyone who stumbles on this later: AMQP only supports getting the number of messages that are “Ready”, not those that are “unacked”. For the latter, you might have to use RabbitMQ’s REST API. See https://stackoverflow.com/questions/63018151/can-i-see-the-count-of-unacked-messages-in-rabbitmq-via-an-amqp-client
My system that consumes from the queue is using Broadway. In normal load, I basically never see any messages as “ready” because they’re quickly grabbed up by my Broadway pipeline. By queueing a lot of messages and putting a
Process.sleep(:infinity)in myhandle_message, I can see that my system will have at most N unacked messages at a time. So if I see any messages in the “ready” count, I can basically assume that there are N more being handled at the moment, which is a good enough indicator to decide whether the system is getting overloaded.