Oracle Integration Cloud: Building Integrations That Survive Production · Module 10 · Business events and publish/subscribe
At-least-once delivery
Lesson 106 of 175 · 2 min
The same event can arrive twice, which is Module 9 again from the other direction. The two modules are one design decision. At-least-once means the delivery mechanism guarantees you will get it, and does not guarantee you will get it once. A redelivery after an acknowledgement was lost, a retry inside the transport, a replay after an outage — all ordinary, and all produce a second copy of an event you have already handled. SO EVERY EVENT SUBSCRIBER MUST BE IDEMPOTENT, and it is the same mechanism as everywhere else: a correlation key that identifies the work, and a constraint or a record that makes the second attempt a no-op. THE KEY IS USUALLY EASIER HERE, which is the one piece of good news. Events typically carry an event identifier and the identifier of the record they are about, so the correlation key is available rather than something you have…
The full lesson is part of the course
The video, the complete written lesson and the module quiz are included in Oracle Integration Cloud: Building Integrations That Survive Production, with a certificate on completion and a fourteen-day refund window.