The Quiet Partition
A hard AI Coding mock interview question on DataDriven, with an AI interviewer who asks follow-up questions and a hire or no-hire decision at the end.
- Domain
- AI Coding
- Difficulty
- hard
- Seniority
- L6
Interview Prompt
Our Flink job aggregates user sessions and writes hourly rollups. Each midnight one source partition (the EU one) falls quiet for ~2 hours during low-traffic. During that window the global watermark stops advancing, no session windows close, and state size grows unbounded until the JM kills the job. Run tests/test_quiet_partition.py to reproduce. Find the watermarking pattern in jobs/sessions.py and fix it. Defend the new behavior: what's the maximum end-to-end latency you've now committed to?
Summary
One went quiet. All of them stopped.
How This Interview Works
- Read the task and the repository: the files, the failing check and the constraints
- Work the fix with the AI agent at your side, and run the checks until they pass
- Submit, then answer the interviewer's questions about the change you made
- Get a hire or no-hire decision with feedback on how you drove the agent