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Advanced Queuing - Oracle

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Gateway Agent<br />

Propagation Processing Overview<br />

The gateway agent schedules and processes propagation jobs. The agent executes in<br />

an external process of the <strong>Oracle</strong> database server. The agent is started and<br />

terminated by calling the STARTUP and SHUTDOWN procedures in the<br />

administration package. Like all external processes of <strong>Oracle</strong> database server, the<br />

agent runs only when the database server that it resides in is up and running.<br />

The agent contains a propagation engine and a set of drivers for the non-<strong>Oracle</strong><br />

messaging systems. The multithreaded propagation engine fairly schedules<br />

propagation jobs and provides parallel interjob and intrajob propagation<br />

processing. A polling thread in the agent periodically polls the source queues of<br />

enabled propagation jobs and wakes up worker threads to process propagation jobs<br />

if messages are available. The drivers in the gateway agent are instantiated when<br />

messaging links are created. The drivers run as clients of messaging systems for all<br />

messaging operations.<br />

The agent writes log messages into its log files, which contain information about<br />

agent configuration, agent status, actions taken by the agent upon receiving<br />

dynamic notifications, status of propagation jobs, and all error messages.<br />

Propagation Processing Overview<br />

You create propagation jobs to set up message propagation. A propagation job<br />

conceptually consists of a propagation subscriber and a propagation schedule.<br />

After a propagation subscriber is created, the gateway creates a subscription on the<br />

propagation source if the source is a topic (publish-subscribe). The gateway moves<br />

all messages that are published to the topic after the subscriber is created. If the<br />

propagation source is a point-to-point queue, the gateway moves all messages in<br />

the queue to the destination.<br />

A propagation job is not processed until an associated propagation schedule is<br />

created. The gateway agent processes enabled propagation jobs. Disabling a<br />

propagation job stops the transfer of messages from the source queue to the<br />

destination queue, but does not stop subscription.<br />

When a propagation job is processed, messages are dequeued in priority order from<br />

the source queue and enqueued to the destination queue. If a message fails to be<br />

converted from the source format to the destination format, the message is moved<br />

to the exception queue. Messages that have expired in a propagation source queue<br />

are not propagated to the destination queue.<br />

Messaging Gateway 18-5

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