Publishing change data
In order to publish data, the publisher (DBA) has to:
Identify the source system (Oracle instance) and the source
tables in which the change data has to be captured.
Have EXECUTE_CATALOG_ROLE and SELECT_CATALOG_ROLE privileges and
privilege to GRANT SELECT on the change tables to the subscribers.
Set up the change data capture system to capture and publish changed
data using DBMS_LOGMNR_CDC_PUBLISH procedures.
Subscribing to change data
Subscribers, typically data warehouse applications that
consume change data, have to:
Identify the source system (Oracle instance) and the source
tables from which the change data has to be captured.
Subscribe to the change tables. The subscriber can access only the
change tables that have SELECT privileges granted to the subscriber by the
publisher.
Activate the subscription, create the subscription window and the
subscriber views to view and query the change data.
Drop and create new subscription windows and subscriber views.
The subscriber does not directly access the change tables and
gets only unique change data from the source tables or the change tables.
To set up change data subscription, the subscriber has to use the
SYS owned DBMS_LOGMNR_CDC_SUBSCRIBE procedures.
If at any time the publisher makes changes to the change tables,
then the subscriber gets appropriate database error exceptions and no message
notifications.
Conclusion
In part three of this series, we discussed Oracles change
data capture features, Oracle Streams and the CDC framework. As mentioned the
CDC feature was introduced in Oracle9.0 while Oracle Streams is the newest
addition to the list of new features.
While Oracle Streams provide a host of features including
change data capture from different databases to messaging notification across a
broad network of databases (or data warehouses, data marts, ODS etc.), CDC is
limited to low volume databases and capturing only DML changes from an Oracle
database.
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