Point-To-Point Messaging (Sun Java System Message Queue 4.1 Technical Overview)

Sun Java System Message Queue 4.1 Technical Overview

Point-To-Point Messaging

In the point-to-point domain, message producers are called senders and consumers are called receivers. They exchange messages by means of a destination called a queue: senders produce messages to a queue; receivers consume messages from a queue.

Figure 2–1 shows the simplest messaging operation in the point-to-point domain. MyQueueSender sends Msg1 to the queue destination MyQueue1. Then, MyQueueReceiver obtains the message from MyQueue1.

Figure 2–1 Simple Point-to-Point Messaging

Message travels from sender to receiver via a queue destination.
Figure described in text.

Figure 2–2 shows a more complex picture of point-to-point messaging to illustrate the possibilities in this domain. Two senders, MyQSender1 and MyQSender2, use the same connection to send messages to MyQueue1. MyQSender3 uses an additional connection to send messages to MyQueue1. On the receiving side, MyQReceiver1 consumes messages from MyQueue1, and MyQReceiver2 and MyQReceiver3, share a connection in order to consume messages from MyQueue1.

Figure 2–2 Complex Point-to-Point Messaging

Two senders use one connection to send messages to one
receiver. Two consumers getting messages from same queue. Figure explained
in text.

This more complex picture illustrates a number of additional points about point-to-point messaging.

More than one producer can send messages to a queue. Producers can share a connection or use different connections, but they can all access the same queue.
More than one receiver can consume messages from a queue, but each message can only be consumed by one receiver. Thus Msg1, Msg2, and Msg3 are consumed by different receivers. (This is a Message Queue extension.)
Receivers can share a connection or use different connections, but they can all access the same queue. (This is a Message Queue extension.)
Senders and receivers have no timing dependencies: the receiver can fetch a message whether or not it was running when the client sent the message.
Senders and receivers can be added and deleted dynamically at runtime, thus allowing the messaging system to expand or contract as needed.
Messages are placed on the queue in the order sent, but the order in which they are consumed depends on factors such as message expiration date, message priority, and whether a selector is used in consuming messages.

The point-to-point model offers a number of advantages:

The fact that multiple receivers can consume messages from the same queue allows you to load-balance message consumption if the order in which messages are received is not important. (This is a Message Queue extension.)
Messages destined for a queue are always retained, even if there are no receivers.
Java clients can use a queue browser object to inspect the contents of a queue. They can then consume messages based on the information gained from this inspection. That is, although the consumption model is normally FIFO (first in, first out), consumers can consume messages that are not at the head of the queue if they know what messages they want by using message selectors. Administrative clients can also use the queue browser to monitor the contents of a queue.