Dynamic suspension of JMS producer

[Baris Acar <ba...@acar.org.uk>]

Hi,

We have two instances of a service, one for low and one for high priority users. Both post messages to a single shared queue, with the appropriate priority level set so that high priority requests jump in front.

If the queue is completely full of low priority requests, it's impossible for high priority requests to arrive. I'd like to prevent this.

One way is to limit the number of low priority messages allowed on the queue. We would like to stop the low priority service posting if the (jms) queue is >90% full. This always leaves some headroom on the queue for some high priority messages. We've had success with this model in other (non-camel) applications.

How best could I do this with Camel? Also very open to completely alternative proposals solving the use case. 

I don't think that there is a JMS-only way to inspect queue depth - we'll have to use vendor-specific code to interrogate queue depth (we use IBM MQ and Solace).

The first ideas I had were:
- use a RoutePolicy to suspend the part of the route that's posting - but casual playing found that suspending in this way caused exceptions rather than blocking behaviour when a route was suspended (I might be doing something wrong).
- write a processor which sits just before the "jms:..." endpoint, which inspects the queue and blocks as appropriate. This seems a bit ugly (it needs to know about specific downstream endpoints, which is "weird"). 

Is there something more Camel-y? Any thoughts or ideas most welcome. 

Barış