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Chapter 3 -
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:
High Speed Replication and Data
by Madhu Tumma
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