Machine Learning System Design Interview, issue 19, Dec 5, 2025
The Database-as-Queue Trap
Machine Learning Engineer interview at Google, and the interviewer asks:
“We have 3 upstream microservices generating features. They write to a central 𝘗𝘰𝘴𝘵𝘨𝘳𝘦𝘴 𝘋𝘉. Your ML Service queries that DB to get the input vector for inference. How do we scale this to 50k requests per second?”
How relying on a persistence layer for real-time inference creates silent bottlenecks, and how event brokers fix them.
The full answer, with the mechanism and the arithmetic, is for paid subscribers on Substack.