https://comparison.metacog.co.kr/tags/idempotency/Recent content in Idempotency on IT ComparisonHugoen-usSun, 06 Sep 2026 09:59:45 +0900https://comparison.metacog.co.kr/posts/2026-09-06-at-least-once-vs-exactly-once-delivery-guarantees-compared/Sun, 06 Sep 2026 09:59:45 +0900https://comparison.metacog.co.kr/posts/2026-09-06-at-least-once-vs-exactly-once-delivery-guarantees-compared/<h2 id="overview">Overview</h2> <p>Messaging and stream-processing systems must pick a delivery guarantee: does a message arrive at least one time (possibly more), or does its effect happen precisely once no matter how many retries occur? <strong class="kw">At-least-once</strong> favors simplicity and throughput by retrying until acknowledged, at the cost of possible duplicates; <strong class="kw">exactly-once</strong> layers on deduplication or transactional coordination so retries never produce a second effect. The choice matters because a duplicate side effect — a double charge, a double email, a double stock decrement — can be catastrophic or merely annoying depending on the domain.</p>