System designHardsd-g030

Subject Consistency tuningLevel Senior–Staff~45 minCommon in Databases & SQL interviewsIndustries Technology, Software development

Question

You operate a Dynamo-style quorum store (replication factor N=3 across 3 regions) backing a globally distributed shopping cart. Most operations tolerate brief staleness, but 'place order from cart' must never undercount or drop an item the user just added. Cross-region round-trips are ~120ms. Design the read/write consistency-level policy per operation, explain how you avoid lost writes and ensure the order path is correct, and describe what conflict resolution and anti-entropy you'd run.

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.