Distributed JMS help using topic - can it do this?

Question

Using Weblogic 10.0, what is the a suggested configuration for having 2 apps in a cluster, where one creates messages in a distributed topic and another (a servlet) reads those messages? Messages need to be acknowleged and removed once read regardless of which managed server the user is on.
          Currently, I have a cluster of managed servers with a Uniform Distributed Topic, and I need a user to read a message just once regardless of which managed server he uses.
          I have 2 Ears - one creates messages, and another is a servlet that allows a user to read a message.
          My reader has a listener that subscribes on startup - like this:
          tconFactory.createTopicConnection(...);
          connection.createTopicSession(...)
          session.createSubscriber (...)
          It does a readNoWait() if a user clicks on a button. Another app puts messages in the topic.
          I want the user to read the message once (any only once) regardless of which managed server he is on.
          The way it is working is that if a user switches from one managed server to another he sees old messages he already read.
          Also, I tried using the module!queuename JNDI name but I get an exception. I have to just use the "regular" topic name.
          Any help appreciated!
          thanks in advance
          Edited by dantill at 05/16/2008 8:12 AM

Answer 1

So in a clustered environment, if a user is reading (and acknowledging) messages from a topic and that user is "load balanced" to another managed server on the cluster, he will see messages he already acknowledged?                     No - things don't work this way, unless the user is attaching to two different durable subscriptions. You may want to pick up a book on JMS, or study up on the Sun tutorials, and pay special attention to the difference between queues and topics, and the difference between "non-durable" and "durable" topic subscribers. It would likely help if you firmed up on these concepts before diving into the concept of distributed topics.
          The key points of WL distributed topics are:
          (1) Durable subscription can only be formed directly on a member (they can't move from member to member!), you can't specify the distributed topic JNDI name when creating a durable subscription - only the member JNDI name.
          (2) Non-durable subscriptions can specify the distributed topic JNDI name.
          (3) Just as with a non-distributed topic, every message that is sent to the distributed topic or that is sent directly to particular member is in turn delivered to every subscribers on every members.
          >>>> About Migratable targets - it may have been this statement:
          "A migratable target is a special target that can serve as a grouping of JMS services and which is active on only server member in a cluster."
          All this means is that multiple JMS services (such as JMS servers) can all target to the same MT. When the MT is migrated from one WL server to another, all related JMS servers are migrated.
          PS. Given my limited knowledge of your use case, it seems like you're looking for a distributed queue (not a topic), with a single consumer that can switch between one of two servers. Or perhaps one consumer on each server. In addition, in order to avoid "abandoning" messages on a particular queue member without consumers, there's a configurable option to have the idle member automatically forward its messages to a queue member that actually has consumers (queue forwarding option).
          Hope this helps,
          Tom