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From James Casey <>
Subject Re: Problems with Virtual Topics
Date Thu, 01 Apr 2010 15:14:52 GMT
On 1 April 2010 16:04, Shyam Santhanam <> wrote:

> There are a few more observations I've made while trying to debug this.
> We've
> noticed that sometimes the messages received from the consumer queues have
> JMSDestination set to the VirtualTopic name, and at other times they have
> the consumer queue name. As shown earlier, I do have the
> excludedDestinations clause necessary to exclude forwarding to the queues.
> Is this still to be expected?
Hi shyam,

we've seen this too - it depends on where the messages were sent to.

Assume you have 2 brokers A and B.

Connect your virtual topic consumer to A.

Now if a message is sent to A, you get the topic name as destination.

If a message is sent to B, you get the queue name as destination.

> Also, looking in JMX at the VirtualTopic's topic MBeans, I've noticed that
> the topics themselves have consumers in addition to the queue. Are these
> consumers created internally by the broker to enable forwarding, or could
> this indicate a problem? Further, there are far many more consumers for the
> topics. For example, when testing with 2 nodes: Although I have only one
> consumer queue attached to the topic, and one consumer  to this topic on
> each node, I notice that the VirtualTopic itself shows 6 consumers. Where
> are these consumers coming from?
> Normally  I see some extra consumers from the network of brokers.  since we
use suppressDuplicateQueueSubscriptions="true" on the network connectors I
normally only see one additional consumer - what is your topology ?

Another observation when looking at the MBeans: the QueueSize of the topics
> appears to increase steadily over time.

Could it be this : <> ?

> When I try to browse the contents of
> the topic, I often find that there are some residual messages (usually far
> fewer messages than indicated by the QueueSize statistic, but > 0
> nonetheless). Again, this doesn't gel with my understanding. I thought that
> the topics themselves are "virtual" which should imply that they don't have
> a persistent cache of messages anywhere? Are the virtual topics themselves
> also persisted? If so, when do messages in the topic get evacuated?
> You can  use the topic as a normal topic - perhaps this is the effect you
see ?  when you subscribe then any  messages received will be sent to your
topic consumer.

> If someone familiar with this area could answer these questions, it could
> really help us make some important decisions about how, and whether, to use
> virtual topics to implement our requirements. Has someone used them
> effectively in a network-of-brokers scenario? If so, can you share the
> specifics of your configuration?
> Well we're in the middle of moving from durable consumer to virtual topics,
so I wouldn't say we've
got a final config yet.  We're basically using the config as mentioned on
the apache web pages.


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