Simple JMS Topics question

Question

I'm a little confused on how JMS will handle messages sent to a
          Topic with Message driven beans attached to it. What I'm unclear
          about is how many message driven beans attached to a topic will
          receive the message. Clearly the semantics are that all subscribers
          receive the message when listening on a Topic. But "how many"
          subscribers are there when you use message driven beans attached to
          a topic?
          Suppose I set up a message driven bean to subscribe to a topic.
          The container can create as many instances as necessary to process
          the message, also controlled by initial-beans-in-pool or max-beans-in-pool
          descriptors. So if I sent a message to the topic, how many instances
          of the message driven bean create to receive the message? It would seem
          that I would want to set up a single message driven bean instance in
          each server, and have multiple servers listening to the same topic,
          if I wanted to publish a message that was received in multiple machines,
          say in a cluster.
          Thanks
          

Answer 1

Each MDB pool (eg each container) will a copy
          of the message and hand it to only one instance, no matter how many
          instances. Or, to put another way, only one instance within an MDB
          pool will receive a copy of a particular message.
          If there are two MDB pools listening to the topic, they each will
          receive a copy of every message sent to the topic.
          If you need to have topic messages divided between two
          MDB pools (without "copies") you will need to use a queue. One way to
          do this is to configure a messaging bridge that forwards
          from the topic to a queue, another way is to write a single
          MDB pool that listens to the topic and sends to the queue.
          Chris wrote:
          > I'm a little confused on how JMS will handle messages sent to a
          > Topic with Message driven beans attached to it. What I'm unclear
          > about is how many message driven beans attached to a topic will
          > receive the message. Clearly the semantics are that all subscribers
          > receive the message when listening on a Topic. But "how many"
          > subscribers are there when you use message driven beans attached to
          > a topic?
          >
          > Suppose I set up a message driven bean to subscribe to a topic.
          > The container can create as many instances as necessary to process
          > the message, also controlled by initial-beans-in-pool or max-beans-in-pool
          > descriptors. So if I sent a message to the topic, how many instances
          > of the message driven bean create to receive the message? It would seem
          > that I would want to set up a single message driven bean instance in
          > each server, and have multiple servers listening to the same topic,
          > if I wanted to publish a message that was received in multiple machines,
          > say in a cluster.
          >
          >
          > Thanks