How WebSphere MQ

A business might require two or more distributed databases to be maintained in step. WebSphere® MQ offers a solution involving multiple units of work acting asynchronously.

The top half of Figure 1 shows a two-phase commit structure, while the WebSphere MQ solution is shown in the lower half, as follows:

The first application writes to a database, places a message on a queue, and issues a syncpoint to commit the changes to the two resources. The message contains data which is to be used to update a second database on a separate system. Because the queue is a remote queue, the message gets no further than the transmission queue within this unit of work. When the unit of work is committed, the message becomes available for retrieval by the sending MCA.
In the second unit of work, the sending MCA gets the message from the transmission queue and sends it to the receiving MCA on the system with the second database, and the receiving MCA places the message on the destination queue. This is performed reliably because of the assured delivery property of WebSphere MQ. When this unit of work is committed, the message becomes available for retrieval by the second application.
In the third unit of work, the second application gets the message from the destination queue and updates the database using the data contained in the message.

Figure 1. Data integrity

It is the transactional integrity of units of work 1 and 3, and the once and once only, assured delivery property of WebSphere MQ used in unit of work 2, which ensures the integrity of the complete business transaction.

If the business transaction is a more complex one, many units of work may be involved.