System designHardsd-g115

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

Question

Design a digital wallet for a ride-hailing app: 80M users, peak ~12,000 debits/sec, mixing real-time ride charges, top-ups, P2P transfers, and authorization holds (a hold reserves funds at trip start and settles for the final fare at trip end). A user must never be able to spend reserved funds, and concurrent debits on the same wallet must not overdraw. Describe the balance model, how holds are represented, and how you keep available-balance correct under heavy concurrency.

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

Loading whiteboard…

Run or narrate your approach, then ask the coach.