Your CDC stream replays a batch and a customer issues a GDPR deletion mid-stream. Keep the silver mirror exactly-once and compliant.
CDC design questions usually stop at the happy-path MERGE. This one stress-tests it: an at-least-once stream that double-delivers, hard deletes, soft deletes for audit, and a GDPR erasure that must physically purge even the bronze change log. The guarantees have to compose.
Updated Aug 2026 · Grounded in real Forward Deployed Engineer interview loops and written to a senior-engineer editorial bar.
CDC design questions usually stop at the happy-path MERGE. This one stress-tests it: an at-least-once stream that double-delivers, hard deletes, soft deletes for audit, and a GDPR erasure that must physically purge even the bronze change log. The guarantees have to compose.
Lead with where the obvious approach breaks, because that is the judgment they are screening for — most candidates jump straight to the happy path and lose the room.
Then walk the failure back through the pipeline in order, naming the one metric the customer's exec sponsor actually cares about before you propose the fix.
