You are reviewing the interfaces of a fictional reservations team before a launch rehearsal. The team can tolerate delayed analytics, but a repeated request must not create a second reservation. It also needs a stable history page when several records share a timestamp. Those promises affect the API contract and row identity more than the number of boxes in the diagram.
Work through the unrelated transfer questions too. Different workloads expose different assumptions: a small database can still have a write race, and a cached redirect can remain stale after a mapping changes. Use the supplied values for the estimate and make each choice with its supporting reason. The final tasks ask you to distinguish cleanup from correctness and to keep excluded work out of scope.