Design a transaction reconciliation system
Design a reconciliation system that matches a company's internal ledger of ~5M daily transactions against external bank/PSP statement files (delivered as daily CSV/MT940 batches, often late, sometimes duplicated, sometimes amended). It must auto-match the high-confidence majority, surface unmatched 'breaks' to ops, and handle many-to-one matches (one bank line for a batched payout of 1,000 internal transactions). Describe the matching pipeline, the data model for match state, and how you handle late/duplicate/amended statement files.
What a strong answer looks like
Clarify scale and constraints first. Propose a clean component breakdown, then go deep on the hard parts (data model, bottlenecks, consistency, failure modes) and name the trade-offs you are making.
Clarify6:00 left
Estimate6:00 planned
Design18:30 planned
Deep dive14:30 planned
Failure10:00 planned
Which questions mattered is sealed until you submit. Telling you now would just be handing over the edge cases.
Run or narrate your approach, then ask the coach.