Durable / Persistent KV Store

Tech Deep DiveDatabricksLast reported January 2026Medium Frequency

Reported: 7× across candidate reports
First seen: March 2025
Last reported: January 2026
Reported outcome: mixed

Problem Overview

Design and implement a durable (persistent) key-value store that survives process crashes and can recover its state on restart. The store must support standard get/put/delete operations. Key requirements include: (1) durability via a Write-Ahead Log (WAL) so data is not lost on crash; (2) WAL compaction to prevent unbounded disk…

5 candidate-reported follow-ups — the exact probes interviewers asked, with the trigger for each
The rest of the problem statement — full requirements, constraints, and edge cases
Approach and trade-offs — what passing candidates did, and the mistakes that sink people

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Verified Source

Every question is reconstructed from multiple independent candidate reports. Verbatim follow-ups, not invented ones.

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Interviewer Follow-ups

The exact follow-ups reported by candidates, with the trigger that prompts each one — plus the mistakes that sink people.