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From ttmdev <joe.fernan...@ttmsolutions.com>
Subject Re: Consuming persistent messages from a non-durable subscriber
Date Fri, 28 Mar 2008 14:06:36 GMT

Your non-durable subscriber will only get those messages that were published
while it is active.  When you bounce the broker it does not retain the
identity of your non-durable subscriber. So when the broker comes back up,
it doesn't consider your non-durable subscriber to have been active when the
persisted messages were published.    

Can you use durable subscribers? If not, look into retroactive consumers or
better yet, virtual topics. With the latter you get the functionality of
both a topic and queue and you don't have to worry about setting up unique
identifiers as you would have to when using durable subscriptions.

http://activemq.apache.org/virtual-destinations.html

http://activemq.apache.org/retroactive-consumer.html

Joe
Goto www.ttmsolutions.com for a free ActiveMQ user guide



Ramit Arora wrote:
> 
> Hi All,
> I have a situation where I have to consume persisent messages from many
> non-durable subscribers. My publishers push persistent messages to a
> topic, which are consumed asynchronously by non-durable subscribers. I am
> using the AMQ Persistence Adapter & CLIENT_ACKNOWLEDGE. If I kill a
> non-durable subscriber & bring it up again, some messages are lost, which
> is expected. But consider the following case:
> 1. Start a publisher publishing persistent messages to a topic.
> 2. Start a non-durable subscriber which is slow compared to the publisher.
> 3. Kill the broker when 100 messages have been published but only 50 have
> been consumed.
> 4. Since the publisher & subscriber are failover clients, they wait for
> the broker to come up again.
> 5. Restart the broker.
> 6. Try to get the remaining 50 messages to the non-durable subscriber.
> 
> Step 6 does not work in both 5.0 & the latest 5.1 snapshot. Shouldn't the
> remaining 50 messages be delivered? The JMS spec says:
> "A JMS provider must deliver a PERSISTENT message once-and-only-once. This
> means a JMS provider failure must not cause it to be lost, and it must not
> deliver it twice. PERSISTENT (once-and-only-once) and NON_PERSISTENT
> (at-most-once)
> message delivery are a way for a JMS client to select between delivery
> techniques that may lose a messages if a JMS provider dies and those which
> take extra effort to insure that messages can survive such a failure.
> There is
> typically a performance/reliability trade-off implied by this choice. When
> a
> client selects the NON_PERSISTENT delivery mode, it is indicating that it
> values performance over reliability; a selection of PERSISTENT reverses
> the
> requested trade-off."
> 
> Queues donot suffer from this problem. Please let me know if I am missing
> something.
> 
> Thanks,
> Ramit
> 
> 
> 

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