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Tracking Database Changes with Oracle Change Data Capture (CDC)

Oracle DBMs better known as the Oracle Database is designed, created, and marketed by the Oracle Corporation. It is a database management system that was first released as a commercial application in 1979. Since then, it has been the backbone of most organizations, offering Online Transaction Processing (OLTP), data warehousing platforms, or a combination of the two. 

The Evolution of the Oracle CDC Technology

Oracle CDC (Change Data Capture) was first launched as a built-in tool in Oracle databases along with its 9i version. It was primarily used to record and monitor all changes in the user tables in a database. These modifications were stored in change tables for use in ETL applications and later processed and transferred to other data warehouses and databases. 

The first version of Oracle CDC worked through triggers placed in source databases. This form of technology though did not find favor with database administrators who considered it to be too invasive. Ultimately, Oracle brought a change to the Oracle CDC, named it Oracle Streams, and released it with the 10g version. 

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This more refined version of Oracle CDC used the redo logs of the source database in combination with an in-built replication tool of Oracle Streams. It was a highly optimized method to detect and move change data to a target data repository without impacting the speed or performance of the source database. Most importantly, the source database was not required to be shut down during the replication activity, saving organizations from system downtime. 

Surprisingly, even though this form of Oracle CDC was well received and became very popular, Oracle Streams was discontinued from the 12c version onwards and no longer supported Oracle CDC. Users had no option but to either look for other CDC solutions or opt to pay for Oracle Golden Gate that came with the Oracle CDC feature out of the box. 

Functioning of the Oracle CDC Technology

The concept of Oracle CDC and the technology behind it is simple in its operation. This software has design patterns for tracking and monitoring changes in a database, helping organizations to take cutting-edge analytical decisions based on those changes. The changes made in the source database can be used for data identification and integration as well as data delivery, thus quickening data warehousing activities across businesses and boosting the quality and performance of databases.  

A critical factor for Oracle CDC becoming the mainstay of enterprises in data management activities is that it is a non-intrusive method for replicating databases without any drop or lag in their performances. Further, replicating databases to the cloud with Oracle CDC is done without any downtime or shutting down of the source database or divesting queries from the source to the target database. Data that has changed since the last replication was done can be extracted from multiple sources and transferred to a data warehouse. 

The most critical capability of Oracle CDC is being able to capture and preserve the state of the data. Hence, the whole process is limited to a specific data warehouse environment and can be started through any database or data repository. There are several alternatives for launching Oracle CDC, from physical storage to application logic either as individual entities or a combination of many system layers. 

Oracle CDC helps businesses that run on the Oracle database to lower data warehousing costs while simultaneously bettering operational efficiencies. This is possible because the CDC feature extracts and replicates all changes to the databases in real-time as soon as they are identified in the source databases.

Oracle CDC Technology


The Present Form of Oracle CDC

In its basic form, Oracle CDC is the technology that is initiated when the data in the source database is changed and any other system like the target database has to take some action based on those changes. The source and the target databases can be the same too and Oracle CDC works equally efficiently even when many CDC solutions are present in the same system. 

It is the Oracle Data Integrator that enables Oracle CDC to recognize the changes made to the data at source. Two modes are supported by the Oracle Data Integrator.

Synchronous Mode

The Synchronous Mode works through triggers that are placed in the source database, ensuring that any changes there are captured immediately. A Data Manipulation Language (DML) activity that can be classified as Insert, Update, or Delete is done by each SQL statement. The changed data so captured is a part of the transactions that have been responsible for the data to change at the source. This form of Oracle comes as a standard feature in the Oracle Enterprise and the Standard editions. 

Asynchronous Mode

The Asynchronous Mode works through redo logs via which the data is moved and the changes are captured after a SQL statement is taken through a DML activity. The changed data does not have any effect on the transactions. This is because the changes are not captured as part of the transactions that changed the tables in the source database. The three Asynchronous Modes of Oracle CDC are HotLog, Distributed HotLog, and AutoLog. CDC feature in this mode is based on the Oracle Streams, since discontinued by Oracle, and has a relational interface to it. 

The working of the two modes is simple and can be easily handled mainly because setting up and configuring the Oracle Data Integrator is fully automated and does not need any human intervention or supervision. The Oracle CDC technology has vastly simplified the replication and migration of databases in organizations. 

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