System designMediumsd-g028

Subject Write ahead logLevel Mid–Senior~40 minCommon in Distributed systems interviewsIndustries Technology, Software development

Question

Design the write-ahead log for a single-node relational OLTP engine that must guarantee durability (committed transactions survive a crash) and atomicity (no torn writes), while sustaining 60k small transactions/sec with a commit-latency p99 under 5ms. The dataset is 500GB on NVMe; in-place page updates are used for the main heap/index. Describe the WAL record format, the commit protocol, how recovery works, and the main throughput trade-off.

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.