System Programming: Multi-Threaded Chat System

Tech Deep DiveDatabricksLast reported January 2026Medium Frequency
Reported
4× across candidate reports
First seen
April 2025
Last reported
January 2026
Reported outcome
mixed

Problem Overview

Implement a single-machine, multi-client chat server shared by many threads. Users can subscribe to several channels; a message sent to a channel is delivered to every current subscriber. Support create channel, subscribe, unsubscribe, send, and receive. This is Databricks' System Programming round, and it tests concurrency, not scale: write the…

  • 3 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.
Codex Fact-Checked
Technical claims, formulas, and scale numbers are reviewed against primary sources.
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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