Problem Statement
Which delivery guarantee is most commonly achievable in distributed messaging at scale?
Explanation
Networks fail and consumers crash; retries can generate duplicates. At-least-once is practical and robust when consumers are idempotent. Exactly-once exists in narrow, coordinated contexts but is complex and slower.
Design handlers to tolerate duplicates and out-of-order events.
Code Solution
SolutionRead Only
if(seen(key)) return storedResult; else process(); markSeen(key)
Practice Sets
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