Distributed
Idempotency Key
A client-generated unique key stored with a uniqueness constraint so a retry replays the stored response instead of re-executing.
Why interviewers ask about it
Insert first and catch the unique violation - never read-then-write, which races. Commit the key and the effect in one transaction.
Related terms
This term is part of the free System Design interview preparation module - browse the full glossary for every definition.