Streams leverages log-based procedures to capture DML or DDL changes or synchronous
capture for DML changes and then uses queuing procedures as part of the staging.
User-supplied ???apply??? rules define consumption.
When changes are captured from an Oracle source database redo log or changes in
rows are gathered from synchronous capture, a background database process creates
a logical change record (LCR). LCR and user message events are enqueued in a
Figure 13-3. Advanced Queuing configuration for publish-subscribe applications
Publisher
Application
Oracle Database Server
with Advanced Queuing / Rules
Engine
Subscriber
Application
Publish Message Subscribe to Queue
316 | Chapter 13: Oracle Distributed Databases and Distributed Data
Streams queue. Events are propagated from source to target queues and then, via a
background process, dequeued in the target database and applied. Since Oracle
Database 10g, downstream capture of changes and enqueue/dequeue of messages in
batch are supported.
Also, since Oracle Database 10g, Streams can be configured to provide Database
Change Notification via email, HTTP, and PL/SQL.
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