Increase concurrency on supported queue of topic:channel - spring-xd

Question

I was testing on SpringXD 1.3.0.RELEASE the duplication of messages to different sinks. My configuration is a three node cluster supported by RabbitMQ as message bus.
My test was something like this:
First Case
stream create sourceToDuplicate --definition "trigger --fixedDelay=1
--timeUnit=MILLISECONDS --payload='test' > topic:test" --deploy
stream create processMessages1 --definition "topic:test > cassandra --initScript=file:<absolut-path-to>/int-db.cql --ingestQuery='insert into book (isbn, title, author) values (uuid(), ?, ?)'"
stream create processMessages2 --definition "topic:test > aggregator --count=1000 --timeout=1000 | file" --deploy
Now in order to increase the consumer on the cassandra-sink, I want to deploy the first stream with "module.cassandra.consumer.concurrency=10". This property let fail the deployment.
My workaround is now a fourth stream, so that I can increase the consumers:
Second Case
stream create topicToQueue1 --definition "topic:test > queue:test1" --deploy
stream create processMessage1 --definition "queue:test1 > cassandra..."
stream deploy processMessage1 --properties "module.cassandra.consumer.concurrency=10"
Finally my question: Why should the first use case fail if there is on rabbitmq already a queue added for the topic:channel where more consumers are allowed?
Merry Christmas to everyone
--- Update ---
Version: SpringXD 1.3.0.RELEASE
Error:
2015-12-18T13:58:28+0100 1.3.0.RELEASE INFO DeploymentSupervisor-0
zk.ZKStreamDeploymentHandler - Deployment status for stream 'processMessage1':
DeploymentStatus{state=failed,error(s)=java.lang.IllegalArgumentException:
RabbitMessageBus does not support consumer property: concurrency for processMessage1.topic:test.
at org.springframework.xd.dirt.integration.bus.MessageBusSupport.validateProperties(MessageBusSupport.java:786)
at org.springframework.xd.dirt.integration.bus.MessageBusSupport.validateConsumerProperties(MessageBusSupport.java:757)
at org.springframework.xd.dirt.integration.rabbit.RabbitMessageBus.bindPubSubConsumer(RabbitMessageBus.java:472)
at org.springframework.xd.dirt.plugins.AbstractMessageBusBinderPlugin.bindMessageConsumer(AbstractMessageBusBinderPlugin.java:275)
at org.springframework.xd.dirt.plugins.AbstractMessageBusBinderPlugin.bindConsumerAndProducers(AbstractMessageBusBinderPlugin.java:155)
at org.springframework.xd.dirt.plugins.stream.StreamPlugin.postProcessModule(StreamPlugin.java:73)
at org.springframework.xd.dirt.module.ModuleDeployer.postProcessModule(ModuleDeployer.java:238)
at org.springframework.xd.dirt.module.ModuleDeployer.doDeploy(ModuleDeployer.java:218)
at org.springframework.xd.dirt.module.ModuleDeployer.deploy(ModuleDeployer.java:200)
at org.springframework.xd.dirt.server.container.DeploymentListener.deployModule(DeploymentListener.java:365)
at org.springframework.xd.dirt.server.container.DeploymentListener.deployStreamModule(DeploymentListener.java:334)
at org.springframework.xd.dirt.server.container.DeploymentListener.onChildAdded(DeploymentListener.java:181)
at org.springframework.xd.dirt.server.container.DeploymentListener.childEvent(DeploymentListener.java:149)
at org.apache.curator.framework.recipes.cache.PathChildrenCache$5.apply(PathChildrenCache.java:509)
at org.apache.curator.framework.recipes.cache.PathChildrenCache$5.apply(PathChildrenCache.java:503)
at org.apache.curator.framework.listen.ListenerContainer$1.run(ListenerContainer.java:92)
at com.google.common.util.concurrent.MoreExecutors$SameThreadExecutorService.execute(MoreExecutors.java:297)
at org.apache.curator.framework.listen.ListenerContainer.forEach(ListenerContainer.java:83)
at org.apache.curator.framework.recipes.cache.PathChildrenCache.callListeners(PathChildrenCache.java:500)
at org.apache.curator.framework.recipes.cache.EventOperation.invoke(EventOperation.java:35)
at org.apache.curator.framework.recipes.cache.PathChildrenCache$10.run(PathChildrenCache.java:762)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471)
at java.util.concurrent.FutureTask.run(FutureTask.java:262)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471)
at java.util.concurrent.FutureTask.run(FutureTask.java:262)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:745)

Answer 1

You can't have concurrency > 1 on a topic: named channel - otherwise each thread will get a copy of the message.
If you want to use concurrency on a named channel, it has to be a queue: so each thread competes for messages.