System designHardsd-g117

Subject ReconciliationLevel Senior–Staff~55 minCommon in Distributed systems interviewsIndustries Technology

Question

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.

Learn the concepts

Narrate your design

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Run or narrate your approach, then ask the coach.