Message selectors

Question

          Two questions:
          1.) Where does the message selector query get executed? Either every subscriber
          gets all messages for the subscribed topic and then runs the selector against
          it, or the server runs the selector on the message before sending it out to the
          subscriber. While it may seem like the latter is preferable, I wonder how much
          performance on the server side will be affected as a result of the server processing
          ALL of the message selectors. If the former is the case, there is obviously more
          network traffic, but the server's processing time is reduced when many messages
          are sent out to many subscribers with message selectors. Does anyone have any
          input on this?
          2.) Are there any plans for Weblogic supporting subscriptions to a hierarchial
          topic? For example, subscribing to cars.* will return messages sent to the topic
          cars.bmw and cars.ford. I know this is not part of the JMS specification, but
          it is a nice addition.
          Thanks.
          Dan
          

Answer 1

          Tom Barnes <[email protected]> wrote:
          >Hi Dan,
          >
          >Answers in-line.
          >
          >Dan Baumbach wrote:
          >
          >> Two questions:
          >> 1.) Where does the message selector query get executed? Either every
          >subscriber
          >> gets all messages for the subscribed topic and then runs the selector
          >against
          >> it, or the server runs the selector on the message before sending it
          >out to the
          >> subscriber. While it may seem like the latter is preferable, I wonder
          >how much
          >> performance on the server side will be affected as a result of the
          >server processing
          >> ALL of the message selectors. If the former is the case, there is
          >obviously more
          >> network traffic, but the server's processing time is reduced when many
          >messages
          >> are sent out to many subscribers with message selectors. Does anyone
          >have any
          >> input on this?
          >
          >If you use the WL topic multicast extension, the former. The former
          >is the
          >obvious choice using multicast, as the server only has one network call
          >to make per
          >message...
          >
          >Otherwise, the latter. The latter is preferable, as otherwise the
          >server would
          >be making one network call be subscriber per message - which is far more
          >heavy-weight.
          >
          >>
          >>
          >> 2.) Are there any plans for Weblogic supporting subscriptions to a
          >hierarchial
          >> topic?
          >
          >This is under consideration.
          >
          >> For example, subscribing to cars.* will return messages sent to the
          >topic
          >> cars.bmw and cars.ford. I know this is not part of the JMS specification,
          >but
          >> it is a nice addition.
          >
          >Yes, topic hierarchies are not part of the JMS specification, but you
          >can emulate them
          >fairly easily, if somewhat inefficiently, by using JMS selectors with
          >a "like" clause.
          > The publisher sets a correlation-id on the message:
          >msg.setJMSCorrelationID("cars.ford");
          > The subscriber sets its selector to "JMSCorrelationID like 'cars.%'"
          >
          >>
          >>
          >> Thanks.
          >> Dan
          >
          >Tom
          >