Idempotency Keys for Exactly-Once Processing
10 days ago
- #message-processing
- #idempotency
- #distributed-systems
- Idempotency keys enable exactly-once processing in distributed systems by identifying and ignoring duplicate messages.
- UUIDs can serve as idempotency keys but require storing all previous keys, which may not be practical for high message volumes.
- UUIDv7 or ULIDs include timestamps, allowing consumers to detect and flag old messages, though they can't confirm duplicates.
- Monotonically increasing sequences simplify duplicate detection for consumers by only requiring storage of the latest key value.
- Generating monotonically increasing keys is challenging for multi-threaded producers, requiring atomic operations to avoid sequence issues.
- Asynchronous message emission and the outbox pattern can help maintain sequence integrity without serializing producer requests.
- Using the database transaction log (e.g., Postgres WAL) to derive idempotency keys leverages existing serialization for efficient, space-saving duplicate detection.
- Choosing between UUIDs and monotonically increasing sequences depends on message volume, tolerance for duplicates, and operational complexity.