duplicate processing of retried requests

Question

duplicate processing of retried requests

SRR Shinka 40

Issue: Some requests are being processed more than once when automatic retries occur, resulting in duplicate records and repeated operations.

Impact: Duplicate processing is affecting transaction consistency and may lead to incorrect data being stored.

Expected Behavior: A retried request should be recognized as a previously processed operation and should not trigger the same action again.

Request: Please advise how we can identify duplicate requests and implement a reliable mechanism to ensure each operation is processed only once, including how to safely validate the solution before applying it in production.

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Answer 1

Hello,

The core of your issue is that the retry logic is not idempotent. When a request is retried, the system re-executes the same operation without verifying whether it has already been processed, which leads to duplicate records. To solve this, you need to implement a deduplication mechanism based on unique request identifiers and enforce idempotency at the application or service layer.

The most reliable approach is to assign a unique, immutable identifier to every incoming request before processing. This identifier should be persisted in a durable store (SQL table, Redis cache, or message broker metadata) along with the operation status. When a retry occurs, the system checks whether that identifier has already been processed successfully. If it has, the retry is ignored or short-circuited. For example, in SQL Server you can maintain a table keyed by RequestId with a constraint on uniqueness. Any duplicate insert attempt will fail, ensuring only one execution per request. In distributed systems, using idempotency keys stored in Redis with SETNX is a common pattern to guarantee single execution.

Validation before production rollout should be done in a controlled staging environment. Simulate retries by artificially injecting transient failures and verifying that the deduplication logic prevents duplicate inserts or operations. Monitor logs to confirm that retries are recognized and skipped. Also, ensure that your retry mechanism (whether it’s in HTTP clients, message queues, or background jobs) respects the idempotency key and does not bypass it.

If your system involves APIs, you should enforce idempotency keys at the API gateway level. For example, when using REST, include a header like Idempotency-Key and persist it server-side. For message queues like Kafka or RabbitMQ, use message IDs and deduplication logic in the consumer.

This is the industry best practice to prevent duplicate processing: every operation must be idempotent, and every request must carry a unique identifier that is validated before execution.

I hope you've found something useful here. If it helps you get more insight into the issue, it's appreciated to accept the answer. Should you have more questions, feel free to leave a message. Have a nice day!

HP.