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Data & Analytics · Advanced

At-Least-Once Delivery

A delivery guarantee that every message is delivered one or more times, so duplicates are possible but loss is not.

Definition

At-least-once is the default for Pub/Sub, Kinesis, SQS standard queues and Kafka consumers that commit after processing. Consumers must be idempotent or deduplicate on a message ID.

Exam tip

If duplicates appear after retries, the system is at-least-once; add deduplication.

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