Transactional Messaging Problem

Question

Hi,
The problem I am facing is, I have multiple publishers that can send the same type of messages to the topics and mutiple subscribers are receiving the messages (many-to-many). Suppose the publisher makes changes to a database row, and then send a message to the topic reflecting that change. At the same time, another publisher makes changes to the same database row and then send a message to the topic. If there is no transaction involved on the publisher side, it is possible that the second publisher's message arrives at subscriber side first. This could potentially cause trouble on the subscriber side. How can I guarantee the order of the messages published into the topic? In a situation where message service is down and my publisher has the ability to resend the message after service is back alive, the message it is sending will obviously out of order. So what is the best approach to this kind of problem? How can I ensure the right order delivered to the other end of message pipe? Thanks.

Answer 1

Hi,
You are right by saying that updating your database and publishing your messages within the scope of a transaction will solve your problem. But however, you need to use the right database transactional model. The best one to go for is the strict serialisation model that will guarantee you that write operations are strictly done sequentially and then that your messages are published in the right order. Note that this model has a certain degree of overhead that you may be able to relax so that to improve performance.
On the messaging side you will need to use a XA compliant JMS provider as well as a transaction manager. You can achieve that by using an app server or you can use a MDS (message driven service) container. For example, Arjuna provides such a container (http://www.arjuna.com/products/arjunams/tutorials/mds/index.html) that is roughly speaking a light weight MDB container that provides you with concurrent message processing as well as container managed transactions. The MDS container comes with a full JTA compliant transaction manager.
Note that in the event of a database or a JMS bus failure you will rollback your transaction and take the necessary action that could simply be re-trying later or waiting for the faulty resource to reboot.
Hope this helps,
Arnaud
www.arjuna.com