Spring JMS Message Listener - DMLC - what is benefit of polling?

Question

I know the DefaultMessageListenerContainer polls by design. And that the receiveTimeout which sets the polling interval defaults to 1 second.

The way I understand it is that the DMLC will issue a get, and waits the 'receiveTimeout' defined interval (1 second) before it times out and issues another get.

From what I have read, we can set this receiveTimout value to a larger value and have NO effect on messages getting picked up from the MQ because the active 'get' will sit on the listener until a message arrives... and once/if the timeout interval expires it will just submit another get which remains active on the queue until a message arrives.

So my questions is, what is the benefit of a smaller receiveTimout interval ? If we are always going to process a message when it arrives, why on earth would we want to poll the queue every second?

We are running many large applications, and the polling is simply running the CPU usage/bill through the roof, and I cannot find a justification for this.

Answer 1

Yes - the 1 second receive timeout can be very CPU intensive with a large number of queues.

The general idea for the DefaultMessageListenerContainer was to wait for a bit (1 second seems to be a very short wait period), and then, if you don't get a message, it actually tears everything down and does a full reconnect. This is kind of a poor-mans error handling. "If I haven't heard from the broker, assume that something is broken, drop everything and reconnect". If the reconnect were not so expensive, it might not be a bad strategy. Or if you have only one queue. Or maybe you are expecting 10 messages a second and do want to reconnect if a second goes by. If you have a reasonable number of destinations, the reconnect traffic can get downright abusive.

For IBM MQ, failures on the JMS connection/session are reliably picked up. You don't have the, "it just sits there not getting any messages for some reason" scenario. So setting the timeout to 10 minutes (whatever) would be fine.

Note that if you are running in a JEE application server, and your JMS connections are managed by the JCA, then that layer is responsible for detecting bad connections and you don't have to worry about it up in the application layer.

With Camel and for SpringBoot GitHub might be useful.