System designHardsd-g376

Subject Double entryLevel Senior–Staff~45 minCommon in Distributed systems interviewsIndustries Technology, Software development

Question

Design the write path for a double-entry ledger where one account is extremely hot: a marketplace's single platform clearing account is credited/debited on every one of ~25,000 transactions/sec, while millions of seller accounts are cold. Postings per transaction must sum to zero, balances must be strictly consistent (no overdraft past the floor), and you cannot let the hot account become a serialization bottleneck. How do you keep correctness while removing the single-row contention?

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.