The Quiet Partition

A hard AI Coding interview practice problem on DataDriven. Write and execute real ai coding code with instant grading.

Domain

AI Coding

Difficulty

hard

Seniority

L6

Problem

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.

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