Skip Headers
Oracle® Streams Advanced Queuing User's Guide
11g Release 1 (11.1)

B28420-02
Go to Documentation Home
Home
Go to Book List
Book List
Go to Table of Contents
Contents
Go to Index
Index
Go to Master Index
Master Index
Go to Feedback page
Contact Us

Go to previous page
Previous
Go to next page
Next
PDF · Mobi · ePub

17 Introducing Oracle Messaging Gateway

The Messaging Gateway administration package DBMS_MGWADM provides an interface for creating Messaging Gateway agents, managing agents, creating messaging system links, registering non-Oracle queues, and setting up propagation jobs.

This chapter contains these topics:

17.1 Introducing Oracle Messaging Gateway

Messaging Gateway enables communication between applications based on non-Oracle messaging systems and Oracle Streams AQ.

Oracle Streams AQ provides propagation between two Oracle Streams AQ queues to enable e-business (HTTP through IDAP). Messaging Gateway extends this to applications based on non-Oracle messaging systems.

Because Messaging Gateway is integrated with Oracle Streams AQ and Oracle Database, it offers reliable message delivery. Messaging Gateway guarantees that messages are delivered once and only once between Oracle Streams AQ and non-Oracle messaging systems that support persistence. The PL/SQL interface provides an easy-to-learn administrative API, especially for developers already proficient in using Oracle Streams AQ.

This release of Messaging Gateway supports the integration of Oracle Streams AQ with applications based on WebSphere MQ 6.0 and TIB/Rendezvous 7.2.

17.2 Oracle Messaging Gateway Features

Messaging Gateway provides the following features:

17.3 Oracle Messaging Gateway Architecture

Messaging Gateway has two main components:

Figure 17-1 shows how these components work together with Oracle Database and non-Oracle messaging systems.

Figure 17-1 Messaging Gateway Architecture

Description of adque449.gif follows
Description of the illustration adque449.gif

17.3.1 Administration Package DBMS_MGWADM

The Messaging Gateway administration package DBMS_MGWADM provides an interface for creating named Messaging Gateway agents, managing agents, creating messaging system links, registering non-Oracle queues, and setting up propagation jobs.

Users call the procedures in the package to make configuration changes regardless of whether the Messaging Gateway agent is running. If the Messaging Gateway agent is running, then the procedures in the package send notifications for configuration changes to the agent. The agent dynamically alters its configuration for most configuration changes, although some changes require that the agent be shut down and restarted before they take effect. All the procedures in the package are serialized to guarantee that the Messaging Gateway agent receives and processes notifications in the same order as they are made.


See Also:

Oracle Database PL/SQL Packages and Types Reference for more information on DBMS_MGWADM

17.3.2 Oracle Messaging Gateway Agent

The Messaging Gateway agent runs as an external process of the Oracle Database server and processes propagation jobs. It is started and shut down by calling the STARTUP and SHUTDOWN procedures in DBMS_MGWADM package.

The Messaging Gateway agent contains a multithreaded propagation engine and a set of drivers for messaging systems. The propagation engine fairly schedules propagation jobs and processes propagation jobs concurrently. The polling thread in the agent periodically polls the source queues of enabled propagation jobs and wakes up worker threads to process propagation jobs if messages are available. The drivers for non-Oracle messaging systems run as clients of the messaging systems for all messaging operations.

17.3.3 Oracle Database

As an Oracle Database feature, Messaging Gateway provides a mechanism of message propagation between Oracle Streams AQ and non-Oracle messaging systems. Oracle Streams AQ is involved in every propagation job as either propagation source or propagation destination.

Messaging Gateway is managed through the PL/SQL administration package DBMS_MGWADM. All configuration information and execution state information of Messaging Gateway are stored in Oracle Database and can be accessed through database views.

The Messaging Gateway agent runs as an external procedure of the Oracle Database server. Therefore, it runs only when its associated database server is running.

17.3.4 Non-Oracle Messaging Systems

The Messaging Gateway agent connects to non-Oracle messaging systems through messaging system links. Messaging system links are communication channels between the Messaging Gateway agent and non-Oracle messaging systems. Users can use the administration package DBMS_MGWADM to configure multiple links to the same or different non-Oracle messaging systems.

Queues in non-Oracle messaging systems, such as WebSphere MQ queues, TIB/Rendezvous subjects, and WebSphere MQ JMS destinations (queues and topics) can all serve as propagation sources and destinations for Messaging Gateway. They are referred to as foreign queues. All foreign queues involved in message propagation as source queues, destination queues, or exception queues must be registered through the administration package. The registration of a foreign queue does not create the physical queue in a non-Oracle messaging system, but merely records information about the queue, such as the messaging system link to access it, its native name, and its domain (queue or topic). The physical queue must be created through the administration interface of the non-Oracle messaging system.

17.4 Propagation Processing Overview

Propagation jobs must be defined in order for messages to be propagated from one messaging system to another. A propagation job defines the source queue, destination queue, and various other attributes that affect the processing of the propagation job.

If the propagation source is a queue (point-to-point), then the Messaging Gateway agent moves all messages in the queue to the destination. If the propagation source is a topic (publish/subscribe), then the Messaging Gateway agent creates a subscription on the propagation source topic. The agent moves all messages that are published to the topic after the subscription is created.

A propagation job is processed when it is enabled. Disabling a propagation job stops propagation processing but does not stop message subscription.

When the Messaging Gateway agent processes a propagation job, it dequeues messages from the source queue and enqueues the messages to the destination queue. As each message is propagated, it is converted from its native format in the source messaging system to its native format in the destination messaging system. Messaging Gateway provides automatic message conversions between simple and commonly used message formats. You can customize message conversions by providing your own message transformation functions.

When the Messaging Gateway agent fails to convert a message from the source format to the destination format, the agent moves the message from the source queue to an exception queue, if the exception queue exists, and continues to process the propagation job.

If the Messaging Gateway agent runs into failures when processing a propagation job, it retries up to sixteen times in an exponential backoff scheme (from two seconds up to thirty minutes) before it stops retrying.

To guarantee reliable message delivery, Messaging Gateway requires logging queues in messaging systems that support transactions and persistent messages. The Messaging Gateway agent uses the logging queues to store the processing states of propagation jobs so that it can restore propagation processing from failures.

17.5 Oracle Streams AQ Buffered Messages and Messaging Gateway

Messaging Gateway does not support propagation of buffered messages. In outbound propagation, the Messaging Gateway agent dequeues only persistent messages from AQ queues. In inbound propagation, the Messaging Gateway agent always enqueues persistent messages into AQ queues.