Message points
A message point is associated with a messaging engine and holds messages for a bus destination. A message point is the general term for the location on a messaging engine where messages are held for a bus destination. A message point can be:
- A queue point
- An alias destination
- A publication point
- A mediation point
For point-to-point messaging, the administrator selects one bus member, which can be an application server or server cluster, to hold the messages of the queue destination. This action automatically defines a queue point for each messaging engine in the assigned bus member.
- For a queue destination assigned to an application server, all messages
sent to that destination are handled by the messaging engine of that server, and message order is preserved.
- For a queue destination assigned to a server cluster, there is a separate message point for each messaging engine in the cluster. The message points partition the destination in the same way that a WebSphere MQ cluster partitions a clustered queue. Multiple messages addressed to a such a partitioned destination are handled by any messaging engine in the cluster, but an individual message is handled by only one messaging engine.
The messages of the destination are split between the separate message stores for the messaging engines. This configuration has the disadvantage that message order cannot be preserved, but has advantages:
- Multiple producers or consumers can be deployed across the same server cluster and messaging operations are handled locally by the messaging engine of a cluster member.
- Cluster monitoring can detect the failure of a messaging engine, and the surviving engines within the cluster can take over the message stores containing the permanent state for the failed engine.
If message ordering must be preserved, follow the rules described in Message ordering.
- Multiple producers or consumers can be deployed across the same server cluster and messaging operations are handled locally by the messaging engine of a cluster member.
Applications can use an alias destination to route messages to a target destination in the same bus or to another (foreign) bus (including across a WebSphere MQ link to a queue provided by WebSphere MQ). By assigning an alias destination to a subset of the queue points of a partitioned queue destination, alias destinations can be used to restrict the queue points used by producing and consuming applications.
For publish/subscribe messaging, the administrator configures a topic space destination, but does not have to assign a bus member for the topic space. A topic space has a publication point defined automatically for each messaging engine in the bus.
Message points can be remote from the application which is producing to or consuming from the bus destination. In other words, message points can be on a messaging engine other than the messaging engine to which the application is connected. In this situation the message point is represented at runtime by a remote message point on the remote messaging engine.
By monitoring message points and remote message points, we can fully analyze and resolve problems arising from distributed application messaging. For example, we can:
- Determine the state of a specific message request.
- Determine the location of a specific message.
- Examine message queues to determine if messages have been sent or received.
- Free or delete message requests that have become locked.
- Delete or move messages from remote message points.
Subtopics
Related concepts