Yeah, RabbitMQ opted for the 2nd because of that. BQ in that case is whatever queue implementation was selected; if you look at both the lqueue.erl and priority

Yeah, RabbitMQ opted for the 2nd because of that. BQ in that case is whatever queue implementation was selected; if you look at both the lqueue.erl and priority_queue.erl, you see that they implemented len() by pulling apart a tuple and taking a value verbatim; no further operations. As such, I'd assume every queue type they support has its own internal wrappers to maintain a length.