System designHardsd-g669

Subject Secondary index service databaseLevel Senior–Staff~45 minCommon in Databases & SQL · Distributed systems interviewsIndustries Technology, Software development

Question

Design a secondary-index service for a sharded primary key-value store (sharded by user_id) that must answer queries by non-key attributes — 'all orders with status=PENDING' or 'all orders in region=EU' — across 200 shards at 60k index reads/sec. The base table takes 40k writes/sec. How do you build and maintain global secondary indexes, and how consistent are they with the base data?

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.