Question

When performing Change Data Capture (CDC) on a high-volume transactional database, which mechanism identifies and extracts only the modified rows without requiring a full table scan or extra load on the source system?

Accepted Answer

The mechanism is transaction log mining. A transactional database records every modification, such as inserts, updates, or deletes, in a sequential file known as a transaction log or redo log. This log is essential for database recovery, ensuring that if the system crashes, it can replay events to return to a consistent state. Because the database writes every change to this log in real time, the log serves as a chronological record of all data modifications. To perform Change Data Capture, a specialized process reads these logs directly from the disk or memory buffers without querying the database engine or scanning tables. This approach is non-intrusive because it bypasses the SQL interface and does not compete with application queries for resources like CPU or memory. By parsing these log files, the CDC process extracts the specific rows and the associated changes, providing a lightweight, near-real-time stream of data updates while maintaining the performance and stability of the source system.

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When performing Change Data Capture (CDC) on a high-volume transactional database, which mechanism identifies and extracts only the modified rows without requiring a full table scan or extra load on the source system?

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