One of our installations have several consumers. These consumers subscribe for messages from a queue linked to a virtual topic. All consumers supply a selector. Some consumers connect, process any persisted messages, then disconnect. These connect/disconnect cycles are repeated a few times a day.
What we've seen is that messages build-up for consumers. These messages does not match the supplied selector. The side effect of this was that we ran into a situation whereby message "got stuck". Increasing the maxPageSize property helped. This is unfortunately a short term solution.
A simple test was constructed whereby selectorAware was set to true:
What we noticed is that:
- Messages are correctly received by a connected consumer
- A consumer that connects, disconnects and re-connects later will loose any messages that were send in the time period it was disconnected.
This behaviour was unexpected. From the AMQ documention (http://activemq.apache.org/virtual-destinations.html):
From version 5.4, dispatch from virtual topics to subscription queues can be selectorAware such that only messages that match one of the existing subscribers are actually dispatched. Using this option prevents the build up of unmatched messages when selectors are used by exclusive consumers
Note: it does not state that the consumer needs to be connected for this feature to work.
Given the test it looks like subscriptions itself are not persisted, thus the AMQ broker has no idea that it should enqueue a message for a particular subscription queue.
Would it be possible to add either of:
- Persist subscription detail, specifically for the case where the subscription's selector should be applied to the subscription queue
- Propagate selectors and the attached subscription queue to the top-level virtual topic so that only interested messages can be delivered to the intended recipient?
Anything else we can try, supply or help with?