System designHardsd-g132

Subject Distributed transactionsLevel Senior–Staff~50 minCommon in Databases & SQL · Distributed systems interviewsIndustries Technology

Question

Design the order placement flow for a high-demand flash-sale system (think limited-stock ticket/sneaker drops): inventory is finite and contended, and an order must reserve stock, then collect payment, then confirm — with payment happening asynchronously (could take seconds to minutes). Reserved-but-unpaid stock must auto-release after a timeout so it isn't lost. Peak ~20,000 reservation attempts/sec on a few thousand SKUs. Describe how you prevent overselling and how you coordinate reserve → pay → confirm consistently.

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.