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Yeah, I'm using it as a transactional outbox to ensure at least once delivery to SNS.

Can't really think of a better way to ensure that a message is always sent if the DB transactions succeeds and is never sent if the DB transaction fails

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You can get so far by ensuring at least once and making everything idempotent (will get you as close to "exactly once" as you can). With a database, the most common pattern is: insert the row for the job, when a worker starts working on it, mark it as in progress so it doesn't get started again, if the task fails, or after some reasonable time-out period, another worker can pick up the task again, ultimately the row for the task is only ever deleted when a worker successfully completes it.

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