ActiveMQ Mirror Queue: Working Example.

If you reached here, you might have already checked few very confusing paragraphs about Mirror queues in ActiveMQ.

Mirror Queues are disabled by default. To enable them, you have to following settings in activemq.xml

<destinationInterceptors>

<mirroredQueue copyMessage = "true" postfix="" prefix="MIRROR."/>

                <virtualDestinationInterceptor>

                                <virtualDestinations>

                                                <virtualTopic name="MIRROR.TEST.>"  prefix="MIR.>." selectorAware="false"/>

                                </virtualDestinations>

                </virtualDestinationInterceptor>

</destinationInterceptors>

               

Out of above: “<mirroredQueue copyMessage = "true" postfix="" prefix="MIRROR."/>” is actually responsible for enabling Mirror Queues.

How ActiveMQ Handles Mirror Queues:

1.       When you enable Mirror Queues, with say prefix as “MIRROR.”, for every queue in the broker one Topic will be created with MIRROR. Prefix.

2.       Now to receive a message from this Topic, Virtual Destinations can be used. More about Virtual Destination can be found here.

Working Example:

                Let’s consider above configuration for prefix for Mirror queues and Virtual Destinations.

1.       Create a queue: TEST.QUEUE

2.       With above settings, Mirror Topic is automatically created as : MIRROR.TEST.QUEUE

3.       Create Virtual Topic Consumer : MIR.COPY.MIRROR.TEST.QUEUE

a.       MIR – Defined Virtual Topic Interceptor

b.      COPY – Name of the Consumer

c.       MIRROR.TEST.QUEUE – is a Topic Name

4.       Send a test message to TEST.QUEUE, same message will appear in MIR.COPY.MIRROR.TEST.QUEUE.

This is complete setting of Mirror Queues.

Problems:

1.       Mirror Topics will be created for Every Queue in the broker

2.       As broker has to track each message from the queue and copy it to topic, further to virtual destination, broker may face performance problem depending on load.