# Four Million Echoes

> It happened. It happened again.

Canonical URL: <https://datadriven.io/problems/four_million_echoes>

Domain: AI Coding · Difficulty: medium · Seniority: L5

## Problem

Our orders enrichment consumer reprocesses ~4M messages every time we deploy. The team added enable_auto_commit=False and explicit commit() calls weeks ago, so this should have stopped. Run tests/test_offsets_persist.py to reproduce. The reprocess window correlates with rebalance events. Find why the explicit commits aren't sticking and fix it. Bonus credit: explain what 'cooperative-sticky' would have changed.

## Related

- [All practice problems](https://datadriven.io/problems)
- [Mock interview mode](https://datadriven.io/interview/four_million_echoes)
- [Data Engineering Interview Prep Guide](https://datadriven.io/data-engineer-interview-prep)
- [Daily Challenge](https://datadriven.io/daily)

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