Advanced Queuing

What Is Advanced Queuing?

When Web-based business applications communicate with each other, producer applications enqueue messages and consumer applications dequeue messages. Advanced Queuing provides database-integrated message queuing functionality.

General Features of Advanced Queuing

A combination of features allows publish-subscribe messaging between applications. These features include rule-based subscribers, message propagation, the listen feature, and notification capabilities.

Enqueue, Dequeue, Propagation Features of Advanced Queuing

A single message can be designed to be consumed by multiple consumers. A queue administrator can specify the list of subscribers who can retrieve messages from a queue. Different queues can have different subscribers, and a consumer program can be a subscriber to more than one queue.

Elements of Advanced Queuing

By integrating transaction processing with queuing technology, persistent messaging in the form of Advanced Queuing is possible. This section defines a number of Advanced Queuing terms.

Basic Components of Advanced Queuing

The following basic components are discussed in this chapter:Data Structures, Enumerated Constants in the Administrative Interface, * Enumerated Constants in the Operational Interface, INIT.ORA Parameter File Considerations.

AQ Programmatic Environments

This chapter describes the elements you need to work with and issues you will want to take into consideration in preparing your Advanced queuing application environment.

Managing Advanced Queue

Configuration information can be managed through procedures in the DBMS_AQADM package. Initially, only SYS and SYSTEM have execution privilege for the procedures in DBMS_AQADM and DBMS_AQ. Users who have been granted execute rights to these two packages will be able to create, manage, and use queues in their own schemas. Users also need the MANAGE ANY QUEUE privilege to create and manage queues in other schemas.

Performance and Scalability

Queues are stored in database tables. The performance characteristics of queue operations are similar to underlying database operations. The code path of an enqueue operation is comparable to SELECT and INSERT into a multicolumn queue table with three IOTs. The code path of a dequeue operation is comparable to SELECT, DELETE, and UPDATE operations on similar tables.

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