Manual Offset Committing
Implement manual control over offset commits to achieve precise control over message processing guarantees and avoid data loss or duplication.
Why Manual Commits?
In Kafka, an offset marks the last message a consumer group has successfully processed from a topic partition. Committing an offset tells Kafka: "I've handled messages up to this point."
By default, Spring Kafka uses auto-commit, where offsets are committed periodically in the background. While convenient, this can sometimes lead to data loss or duplication if your application crashes mid-processing.
Manual offset committing gives you precise control, allowing you to decide exactly when an offset is marked as processed. This is crucial for ensuring message processing guarantees.
Auto-Commit: A Quick Look
With auto-commit, Kafka automatically commits offsets at a set interval (e.g., every 5 seconds). This means:
- Messages are processed.
- Offsets are committed later by Kafka.
If your application processes a message but crashes *before* Kafka's auto-commit interval passes, that message's offset might not be committed. When the application restarts, it will re-read and re-process that message, leading to potential duplicates (at-least-once processing).