The Oracle DBMS or the Oracle Database Management System is produced and marketed by Oracle Corporation and was first released as a commercial application in 1979. Since then, it has been used primarily for running Online Transaction Processing (OLTP), Data Warehousing (DW), or a combination of the two. 

The Concept of Oracle CDC

The technology behind Oracle CDC (Change Data Capture) is used to track and monitor changes made to a database so that the required action may be taken based on them. Oracle CDC is software design patterns that integrate, identify, and deliver data of any changes made to the source database. This leads to a manifold increase in the quality and performance of databases as Oracle CDC, through real-time data integration, speeds up data warehousing facilities. 

Oracle CDC is the ideal tool non-intrusive tool for replicating databases. The activities that can be done with this technology include database migration from on-premises to the cloud or between one cloud provider to another without offloading queries for analytics from databases to data warehouses. 

Further, during replication, the source database remains fully functional, a big help for large data-driven organizations for whom downtime even for brief periods might upset operating schedules. It also enables businesses to extract incremental data from different sources and migrate it to a data warehouse. 

Among the most critical aspects of Oracle CDC is the capability to capture and preserve the format of the data. This helps to confine the activity of replication to a data warehouse environment that can be carried out in any data storage repository or database. Launching Oracle CDC is quick and seamless as several options can be used like application logic or physical storage, either as individual entities or a combination of many system layers. 

The Development of Oracle CDC

The Change Data Capture feature of Oracle was first introduced in 2001 in the 9i version almost two decades after the database management system was officially introduced. In the first models, the functioning of Oracle CDC was through triggers located on the tables in the source database. This technology did not run for long as Database Administrators found it to be quite complex.  

This issue was set right by Oracle in the 10g version with a complete overhaul of the previous technology. Here, Oracle banked on redo logs for its Change Data Capture feature. It was used in combination with Oracle Streams which was a replication tool of Oracle. It helped users to capture and send all changes made at the source database to the target database without using triggers.   

Even though this log-based Oracle CDC gained wide popularity among businesses that found it very useful and user-friendly, Oracle surprisingly withdrew support from the CDC. However, it was still possible to use the Change Data Capture feature that came out of the box with Oracle Golden Gate, a paid and very expensive software for replication.  

Functioning of Oracle Change Data Capture

For Oracle CDC to function optimally, it is essential that the necessary infrastructure and journalizing models be set up and configured so that it will be possible to capture and record the changes made to the current database. The Oracle Data Integrator provides support to two journalizing modes. One is the Simple Journalizing mode where all changes to a particular datastore are identified. The other is the Consistent Set Journalizing mode. Here, as distinct from the previous mode, all changes made to the datastore in a group are identified and referential integrity of the data stores is maintained. 

Database Extraction with Oracle CDC – The Benefits 

There are several benefits of database extraction that organizations can avail of with the Oracle CDC. 

First, and this is very important, with Oracle CDC any changes made in the source tables can be instantly extracted for Insert, Delete, and Update activities in real-time. Without CDC for database extraction, Insert activity cannot be done while the procedures are very complex for Update and Delete due to paucity of data. Further, Oracle CDC places flat files that are not required for staging data directly in relational tables. Without this CDC feature, complete tables would have to be moved into flat files. 

Finally, the user-friendly interface of Oracle CDC is available through DBMS_LOGMNR_CDC_PUBLISH and DBMS_LOGMNR_CDC_SUBSCRIBE packages. In its absence, a lot of manpower would have been required to handle CDC.  

Oracle Change Data Capture Modes

The Oracle Data Integrator is used by the Oracle CDC for identifying any changes made to the source database. Two modes are present in the Data Integrator.  

Synchronous Mode

This mode works through triggers that are placed in the source database with any changes being captured immediately. Each SQL statement that includes Insert, Update, and Delete actions goes through a Data Manipulation Language (DML) activity. The changed data often called incremental data is captured as a part of the transactions that changed the data in the source database. This form of Oracle CDC is available as a standard feature in the Oracle standard and Oracle Enterprise editions. 

Asynchronous Mode

In this mode, the data is first transferred to the redo log files from where the changes have been made after the SQL statement had gone through a DML activity. Since the data has not been captured as a part of the activities that resulted in the changes in the source table, the transactions of the modified data are not affected in any way. There are three options for the Asynchronous mode. They are HotLog, Distributed HotLog, and AutoLog. This mode of Oracle CDC works on the platform of the now-discontinued Oracle Streams. 

These are some of the optimized functionalities of Oracle CDC.