Design a Inventory Management Service
Last updated: September 2, 2025
Quick Overview
Design a high-throughput inventory management system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Citadel
September 2, 202531
15
869 solved
Design a high-throughput inventory management system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Citadel asks this during the Onsite to assess your understanding of the full ML lifecycle. They want to see how you translate a business problem into an ML objective, design the feature pipeline, and plan for model monitoring and retraining.
What the Interviewer Expects
- Design the full ML lifecycle from data collection to model monitoring
- Address cold start, exploration/exploitation, and model freshness
- Discuss multi-objective optimization and ranking systems
- Plan for model debugging, fairness, and bias mitigation
- Design the feature store and training pipeline for scale
- Address model versioning, canary deployments, and rollback strategies
- Discuss the data flywheel and long-term system evolution
Key Topics to Cover
How to Approach This
- Start by clarifying functional and non-functional requirements with the interviewer.
- Estimate the scale: QPS, storage, bandwidth. This drives your design decisions.
- Draw a high-level architecture first, then deep dive into 1-2 critical components.
- Discuss trade-offs explicitly (e.g., consistency vs availability, SQL vs NoSQL).
- Address failure scenarios, monitoring, and how the system handles 10x traffic spikes.
Possible Follow-up Questions
- How would you ensure fairness and reduce bias in the model?
- How would you debug a model that works well offline but poorly online?
- What would you do if model performance degrades over time?
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Requirements
- Functional Requirements:
- Real-time inventory updates for products across multiple locations.
- Support for high-throughput requests (up to millions of transactions per day).
- Provide AP...
Capacity Estimation
To estimate capacity for Citadel's inventory management system:
- Assume 10 million active products, each receiving an average of 100 requests per day.
- Total daily requests = 10,000,000 products * 1...
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