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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