I have a .NET application that uses Apache.NMS to communicate with an ActiveMQ 5.11 server. I noticed via the ActiveMQ console that there were 15k messages pending.
What was odd about this was there was, in fact, a consumer on the queue and it was pulling messages new messages off the queue (being inserted by another end point).
On the surface this seems like a potential ActiveMQ bug. How is it possible for new messages to get "in front of line" on the server and pulled off by my application and yet 15k pending messages just sit there?
As a test, I restarted my application which, as part of it's initial startup, will remove all existing messages from a queue. Doing that seem to get things back in a good state and sure enough it pull all 15k messages off the queue and then proceeded to function normally.
