Let us start with the concept of Oracle Change Data Capture and the technology behind it.
Functioning of Oracle CDC (Change Data Capture)
Oracle CDC is a software pattern that tracks and monitors changes made to a database. Based on them, organizations can take cutting-edge business decisions. The changes made in the source database are used for data identification, integration, and data delivery. This helps to boost data warehousing performance across organizations and speeds up operations.
One of the primary reasons why Oracle Change Data Capture is much preferred by organizations is that it is a non-intrusive method for replicating databases. Additionally, databases can be replicated to the cloud with Oracle Change Data Capture without shutting down the source database or divesting queries from the source to the target database.
This is very useful for large enterprises for whom shutting down databases, even for brief periods during data transfer, can upset operating efficiencies. Moreover, with Oracle CDC, incremental data, that is, data that has been generated after the last replication, can be extracted from several sources and transferred to a destination data warehouse.
Among the critical capabilities of Oracle CDC is capturing and preserving the state of the data. The process can be initiated through any data storage or data repository and is limited to a specific data warehouse environment.
Users have several options for launching Oracle Change Data Capture. These include physical storage and application logic, either as a standalone entity or a combination of the two. Businesses that run on the Oracle Database Management System (DBMS) can use this technology to reduce data warehousing costs while boosting database speed and performance.
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.
The Development of Oracle Change Data Capture
Oracle Change Data Capture was first launched as an out-of-the-box product with the 9i version of Oracle DBMS. Its core function was to record and monitor all changes made in user tables of databases, which were then stored in change tables to be used in ETL applications. Whenever needed, they could be processed and transferred to other data warehouses and target databases.
The technology behind this form of Oracle CDC was quite simple. Triggers were placed in the source databases that were set off whenever a change was identified. However, this product was found to be too intrusive and complex, feedback that made Oracle make changes to it and release it with their 10g version. This software pattern was named Oracle Streams.
This updated Oracle Change Data Capture used the redo logs of the source database in combination with an in-built replication tool of Oracle Streams. This technology enabled users to keep the databases functioning during the replication process.
This product was very well received and became very popular. However, surprisingly, even after the positive reviews, Oracle decided to discontinue Oracle Streams from its 12c version. This left users with no other choice but to pay to use this feature in Oracle Golden Gate, which was available with Oracle CDC as a built-in tool.
Benefits of Oracle Change Data Capture
Before going to the benefits of Oracle CDC, let us learn more about this product in its present form.
Oracle CDC is the user technology that is initiated when there is a change in the data in the source database. At this stage, another system like a target database must take some action based on those changes. While the source and the destination databases are typically different, Oracle Change Data Capture works equally efficiently if both coexist within the same system.
We will now come to the three cutting-edge benefits of using Oracle Change Data Capture.
- Quick data extraction
Oracle CDC enables any changes made in the source tables to be instantly extracted for Insert, Delete, and Update activities in real-time. Without this Oracle tool for data extraction, the Insert activity cannot be performed, while the procedures are very complex for Update and Delete due to a lack of necessary data.
- Placement of flat files
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.
- User-friendly interface
Oracle CDC has a user-friendly interface that is available through DBMS_LOGMNR_CDC_PUBLISH and DBMS_LOGMNR_CDC_SUBSCRIBE packages. If not for Oracle Change Data Capture, using this feature would be very complex.
Functioning Modes of Oracle Change Data Capture
Oracle CDC identifies the changes made to the data at source through the Oracle Data Integrator. It supports two modes of Oracle Change Data Capture.
Synchronous Mode
In the Synchronous Mode, triggers are placed in the source database. This ensures that any changes made in the database are captured immediately in real time. To do so, the Data Integrator uses a SQL Statement to carry out a Data Manipulation Language (DML) activity, which may be classified as an Insert, Update, or Delete.
The captured data is a part of the transactions that have helped the data change at the source. The Synchronous Mode of Oracle CDC is available as a built-in tool in the Oracle Enterprise and the Standard editions.
Asynchronous Mode
In the Asynchronous Mode, redo logs move the data and the changes that are captured after a SQL statement is executed through a DML activity. The changed data does not have any effect on the transactions because the changes are not captured as part of the transactions that changed the tables in the source database.
Since configuring the Oracle Data Integrator is fully automated, the functioning of the two Modes is easy and seamless. Overall, Oracle Change Data Capture has greatly simplified the process of data replication and migration in organizations.