System designHardsd-g122

Subject LedgerLevel Senior–Staff~50 minCommon in Distributed systems interviewsIndustries Technology

Question

Design a multi-currency ledger for a cross-border money app where a user holds balances in 30+ currencies and can convert between them at a quoted rate. ~6,000 conversions/sec. Each conversion debits one currency balance and credits another at a locked FX rate, and the company books a spread as revenue. Describe the data model, how you avoid rounding/precision errors that leak or create money, and how you keep per-currency balances correct and reconcilable.

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.