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Oracle Streams
Chapter 3 - Streams Replication

Local and Down Streams Capture

Figure 3.1 - Local Capture Configured at Source Database

 

Figure 3.1 presents a local capture configuration. In this method, the Capture process runs on the database where the redo logs are produced.

In the Down Streams Capture method, the archived redo log files from the source database are copied to the downstream database.  The Capture process captures changes from these files at the downstream database. The archived redo log files can be copied to the downstream database using a variety of means. They include log transport services, the dbms_file_transfer package, a File Transfer Protocol (FTP), or some other mechanism.

The Down Streams database is not any particular database. It is another stand alone Oracle Instance in which the Capture process, queues, and other propagation processes are configured to run. Figure 3.2 shows the Down Streams capture configuration. This way, the Capture process overhead is effectively shifted from the primary database system.

Figure 3.2 - Capture Configured at a Down Streams Database

 

There is an important distinction between local capture and the Down Streams method. In the local capture method, Capture reads the redo log files, and at times may read archived redo log files. In the case of Down Streams capture, it is always the archived redo files that are read by the Capture process. This is because the redo log files can be copied from the source database to the intermediate database only after they are archived. In this case, there will be a definite latency in the replication process.


The above text is an excerpt from:

Oracle Streams
High Speed Replication and Data Sharing

ISBN 0-9745993-5-2

by Madhu Tumma
 


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