System designHardsd-g024

Subject B treeLevel Senior–Staff~50 minCommon in Databases & SQL · Concurrency · Algorithms & data structures interviewsIndustries Technology, Software development

Question

Design the on-disk B+tree index structure for a single-node embedded OLTP store (think SQLite/LMDB class) that must support fully ACID transactions, crash safety without a separate WAL if possible, and many concurrent readers that never block a writer. Workload is 95% point lookups and short range scans, 5% updates, dataset ~200GB on a single NVMe drive, p99 read latency target 2ms. Walk through the page/node layout, how you achieve durability and reader/writer concurrency, and the central trade-off of your design.

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.