Change data capture: streaming database changes to the rest of your system

Change data capture lets you stream every insert, update, and delete from your database to other systems in real time. CDC is the foundation of event-driven architectures, real-time analytics, and cache invalidation. When implemented well, it's invisible to your application code.

CDC works by reading the database's transaction log. PostgreSQL has the write-ahead log, MySQL has the binary log, and DynamoDB has DynamoDB Streams. A CDC connector reads these logs and publishes the changes as events. Debezium is the most popular CDC platform.

The simplest use case is cache invalidation. When a record is updated in the database, CDC captures the change and publishes an event. Your cache layer subscribes to these events and invalidates the relevant cache entry. This eliminates the need for TTL-based cache invalidation.

CDC enables real-time analytics without performance penalties. Your application writes to the database normally. CDC captures the changes and streams them to an analytics database like ClickHouse. The primary database never sees the analytics query load.

Use CDC for cross-service data synchronization. When service A updates a record, CDC captures the change and publishes it to a message queue. Service B subscribes and updates its own data store. This keeps services decoupled.

CDC introduces a separate infrastructure component that needs to be reliable. If the CDC connector falls behind, your downstream systems are stale. Monitor replication lag and set up alerts. Have a plan for re-syncing downstream systems if the pipeline needs rebuilding.

Start with a single use case. Cache invalidation is a good first use case because the cost of a failure is limited to serving slightly stale data.

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Rizwan Saleem | https://rizwansaleem.co