Sun Java System Message Queue 4.3 Technical Overview

Message Delivery Services

Once clients are connected to the broker, the routing and delivery of messages can proceed. In this phase, the broker is responsible for creating and managing different types of physical destinations, for ensuring a smooth flow of messages, and for using resources efficiently. The broker properties related to routing and delivery are used by the broker to manage these tasks in a way that suits your application’s needs.

Physical Destinations

A physical destination on the broker is a memory location where messages are stored before being delivered to a message consumer. There are four kinds of physical destinations:

Managing Destinations

Managing a destination involves one or more of the following tasks:

Management tasks vary with the kind of destination being managed: admin-created, auto-created, temporary, or dead message queue. For example, temporary destinations do not need to be explicitly destroyed; auto created properties are configured using broker configuration properties which apply to all auto-created destinations on that broker.

Configuring Physical Destinations

For optimal performance, you can set properties when creating or updating physical destinations. Properties that can be set include the following:

For a queue destination you can also configure the maximum number of active and back up consumers and you can specify (for broker clusters) whether delivery to a local queue is preferred.

You can also configure the limits and behavior of the dead message queue. Note, however, that default properties for this queue differ from those of a standard queue.

Managing Memory

Destinations can consume significant resources, depending on the number and size of messages they handle and on the number and durability of the consumers that register; therefore, they need to be managed closely to guarantee good messaging service performance and reliability.

You can set properties to prevent a broker from being overwhelmed by incoming messages and to prevent the broker from running out of memory. The broker uses three levels of memory protection to keep the message service operating as resources become scarce: destination limits, system-wide limits, and system memory thresholds. Ideally, if destination limits and system-wide limits are set appropriately, critical system-memory thresholds should never be breached.

Destination Message Limits

You can set destination properties to manage memory and message flow for each destination. For example, you can specify the maximum number of producers allowed for a destination, the maximum number (or size) of messages allowed in a destination, and the maximum size of any single message.

You can also specify how the broker should respond when any such limits are reached: to slow producers, to throw out the oldest messages, to throw out the lowest-priority messages, or to reject the newest messages.

System-Wide Message Limits

You can also use properties to set limits that apply to all destinations on a broker: you can specify the total number of messages and the memory consumed by all messages. If any of the system-wide message limits are reached, the broker rejects new messages.

System Memory Thresholds

Finally, you can use properties to set thresholds at which the broker takes increasingly serious action to prevent memory overload. The action taken depends on the state of memory resources: green (plenty of memory is available), yellow (broker memory is running low), orange (broker is low on memory), red (broker is out of memory). As the broker’s memory state progresses from green to red, the broker takes increasingly serious actions: