Release 10.1A: OpenEdge Development:
Messaging and ESB

> ## Point-to-Point (PTP) messaging

> Point-to-Point, or PTP, is a domain of JMS messaging in which an application referred to as a sender sends a message to a destination called a queue. Another application, known as a receiver, receives that message from the queue. Messages in a queue are delivered in First-In, First-Out (FIFO) order. Once a message is delivered and acknowledged, the broker removes the message form the queue.

> ##### Sending and receiving messages

> Table 2–1 describes the tasks performed to send and receive messages using PTP messaging.

> Table 2–1: PTP messaging tasks
> Step | Who | What
> --- | --- | ---
> 1. | Receiver | Binds to a queue.1
> 2. | Sender | Creates and populates a message.
> 3. | Sender | Sends the message to the queue.
> 4. | Message broker | Removes the message from the queue and delivers it to the receiver.
> 5. | Receiver | Consumes the message.
> 6. | Receiver | Acknowledges message receipt to the broker.
> 7. | Message broker | Deletes the message after it is acknowledged.

> 1Before starting your session, queues must be defined.

> ##### PTP messaging options and features

> Table 2–2 describes the features of the PTP messaging model.

> Table 2–2: PTP messaging features
> Feature | Description
> --- | ---
> Message delivery | Ensures a message is delivered only once to a single Message Consumer. The first message received by the broker is the first message delivered. This First In, First Out (FIFO) technique causes subsequent messages to endure until the previous message is consumed. Messages wait for a consumer until the message expires.
> Message persistence | Persist messages on a queue based on the maximum size and threshold for the queue. The message remains even if the broker shuts down.
> Static messaging queues | Messaging queues are created.
> Single Message Consumer | There is only one Message Consumer for a given message. Many consumers can listen or receive on a queue, but only one takes delivery of a specific message.
> Message acknowledgement | When the message is acknowledged as delivered by the consumer, it is removed from the queue permanently. No one else sees it and no one else receives it.
> Prefetch count and threshold | A receiver can specify how many messages are to be delivered at a time.
> Queue browsing | A receiver can look at the contents of messages on a queue without consuming the messages.

> For more information, see the "Using PTP messaging" section.

> ##### Building scalable server architecture with PTP queuing

> A typical use of PTP messaging is to build a scalable and reliable server architecture. Both 4GL and non-4GL clients send requests to a JMS queue on a broker. 4GL servers remove messages from the queue, execute the requests, and reply to the clients. Requests and replies do not get lost in the event of a system failure. Scalability is achieved by providing an increasing number of 4GL servers as the number of clients and the rate of requests increases. For an example, see Appendix B "Messaging Examples."

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