Set - 3

Question 11 :

What are pending messages in the console?

Answer :

Pending means the message could have been:
* sent in a transaction but not committed.
* received and not acknowledged.
* received and not committed.
* subject to a redelivery delay (as of WebLogic Server 6.1).
* subject to a delivery time (as of WebLogic Server 6.1).
A rolled back message remains pending until the transaction actually rolls back. Rolling it back multiple times does not cause double counting, nor does an exception that set a transaction as rollbackOnly followed by an actual rollback.
Current implies messages that are not pending.
Total implies total since server last started. The byte counts only consider the payload of messages which includes the properties and the body but not the header.


Question 12 :

How do I use a less than or greater than on a message selector in ejb-jar.xml?

Answer :

Enclose the selector in a CDATA section. That will prevent the XML parser from thinking that less than or greater than is a tag.


'user' ]]>


Question 13 :

Is it better to have more or fewer sessions for a given number of subscribers?

Answer :

Using N sessions for N subscribers gives you concurrency up to N simultaneous threads of execution provided you have as many threads to work with. Each Session gets its own thread as long as there are enough threads available. Otherwise, the sessions serially reuse the available threads.
One session for N subscribers serializes all subscribers through that one session. If the load is heavy they may not be able to keep up without the extra threads.
If you are using CLIENT_ACKNOWLEDGE, N sessions gives you N separate message streams that can be individually recovered. Having one session crosses the streams giving you less control.


Question 14 :

Are foreign destinations handled within foreign JMS messages?

Answer :

WebLogic Server JMS does not know what to do with foreign destinations that it runs into. This issue has been discussed with Sun and the JMS specification does not clearly define destinations well enough for vendors to interoperate at that level. They agree that it is sufficient not to handle foreign destinations preferably in such a way that sending/receiving still work. For WebLogic Server JMS, if you do a setJMSdestination (you should not because it is only for the provider to set it) with a foreign destination, it gets ignored (set to null). Similarly, if you do a setJMSReplyTo for a foreign destination, WebLogic Server JMS will ignore it (set it to null).


Question 15 :

What is the standard way to create threads, do initialization, etc. within the application server?

Answer :

Threads should generally not be created by the user directly is because things may not work correctly. User-created threads do not have some of the thread-local variables pre-set by WebLogic when it creates it's own execute threads, the associated transaction context, or the environment such as the proper class loader. The WebLogic-specific way of doing this is with a startup class or using the WebLogic Time Services. The portable way to do this is to define a load-on-startup servlet, doing the initialization in the init() method and the cleanup in the destroy() method. The servlet itself does nothing. This approach also allows for undeploy/redeploy of the application without restarting the server, including proper cleanup/initialization each time. It also providers more dynamic management of the dependent classes without restarting the server.