Mitigating DB Lock Contention and Race Conditions in Asynchronous Webhook Ingestion

In event-driven architectures, deduplicating asynchronous webhooks often relies on a simple application-level pattern: checking if an incoming event_id exists in the database before processing. However, this naive approach introduces a classic Check-Then-Act race condition (TOCTOU) when executed as an uncoordinated SELECT followed by an INSERT. Under high load, this can lead to duplicate processing or crashes.

To address this issue, a three-tier defense pipeline is proposed. The first layer involves acquiring an immediate exclusive lock to prevent concurrent access. If the lock cannot be obtained, an exponential backoff with jitter is used for retrying the operation. The second layer enforces a database-enforced unique constraint on the event_id field, offloading race resolution to the storage engine's atomic index management.

If a duplicate key violation occurs, the worker safely rolls back the transaction, treating the event as an idempotent no-op. The third layer handles contention and recovery, implementing exponential backoff with jitter for lock contention scenarios.

This layered approach ensures true idempotency under concurrency by relying on atomic database-level constraints and explicit transaction isolation levels or exclusive locks. By implementing these measures, systems can effectively mitigate DB lock contention and race conditions in asynchronous webhook ingestion.