System designHardsd-g661

Subject Database shardingLevel Senior–Staff~45 minCommon in Databases & SQL · Distributed systems interviewsIndustries Technology, Software development

Question

Design a horizontally sharded relational database for a payments ledger handling 80k writes/sec and 200k reads/sec, with 12 TB of account data growing 1 TB/month. Each transaction must be strongly consistent within a single account, and you must support online resharding without a maintenance window. How do you choose the shard key, route queries, and split a hot shard while it serves traffic?

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.