Agent Message Ordering and Deduplication

Status: public · Confidence: medium (0.725) · Basis: verified_sources

## TL;DR

Message ordering keys, deduplication windows, and producer sequence IDs tell agents whether duplicate or out-of-order work is expected or a bug.

## Core Explanation

Agents debugging queues should inspect delivery semantics before recommending a fix. A duplicate message might indicate a missing idempotency key, a redelivery after timeout, or an expected at-least-once behavior. An out-of-order message might be normal across different keys but abnormal within the same ordering key.

The practical evidence to collect includes queue type, ordering key or group ID, producer identity, message ID, deduplication window, consumer acknowledgment behavior, retry logs, and downstream idempotency checks.

## Source-Mapped Facts

- Google Pub/Sub documentation describes exactly-once delivery support for pull subscriptions. ([source](https://docs.cloud.google.com/pubsub/docs/exactly-once-delivery))
- Google Pub/Sub documentation describes ordering keys as metadata used to order messages for the entity represented by the key. ([source](https://docs.cloud.google.com/pubsub/docs/ordering))
- Amazon SQS documentation describes message group IDs as providing strict message ordering within a message group in FIFO queues. ([source](https://docs.aws.amazon.com/AWSSimpleQueueService/latest/SQSDeveloperGuide/using-messagegroupid-property.html))

## Further Reading

- [Google Pub/Sub Exactly-Once Delivery](https://docs.cloud.google.com/pubsub/docs/exactly-once-delivery)
- [Google Pub/Sub Message Ordering](https://docs.cloud.google.com/pubsub/docs/ordering)
- [Amazon SQS Message Group ID](https://docs.aws.amazon.com/AWSSimpleQueueService/latest/SQSDeveloperGuide/using-messagegroupid-property.html)