On Idempotency Keys

Explores strategies for implementing idempotency keys in distributed systems to achieve exactly-once message processing. Compares UUIDs (with timestamp variants like UUIDv7) against monotonically increasing sequences, examining their trade-offs in storage efficiency and implementation complexity. Presents a log-based approach using Change Data Capture and database transaction logs (particularly Postgres WAL) to generate monotonically increasing keys without serializing producer requests, combining the benefits of both approaches through the outbox pattern.