In-Memory KV Cache with WAL Log

System DesignDatabricksLast reported July 2026Medium Frequency
Reported
6× across candidate reports
First seen
June 2025
Last reported
July 2026
Reported outcome
mixed

Problem Overview

Design an in-memory key-value (KV) cache/store for a web service. The core requirements are: 1. Basic interface: put(key, value) and get(key) operations on an in-memory hash map. 2. Durability via Write-Ahead Log (WAL): before applying any mutation, write it to a WAL file so the store can recover after a…

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