Design a Recommendation Service
Last updated: March 19, 2026
Quick Overview
Design a multi-tenant recommendation system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Notion
March 19, 202647
5
1,940 solved
Design a multi-tenant recommendation system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
This fundamentals question from Notion's System Design Round tests whether you can reason about software design at a deep level. The interviewer expects discussion of maintainability, testability, and operational considerations.
What the Interviewer Expects
- Explain the concept clearly with a practical example
- Discuss when and why to apply this principle
- Identify common mistakes and anti-patterns
- Compare with alternative approaches
Key Topics to Cover
How to Approach This
- Apply SOLID principles. Single Responsibility makes code testable, Open/Closed makes it extensible.
- Choose data structures based on access patterns, not familiarity.
- Prefer immutable data and message passing over shared mutable state for concurrency.
- Design APIs with RESTful conventions, versioning, meaningful errors, and pagination from day one.
Possible Follow-up Questions
- How would you document this for other engineers?
- How would you handle backward compatibility?
- How would you measure the performance of this component in production?
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Core Design Principles
For the recommendation service at Notion, the core design principles are Separation of Concerns, Scalability, and Loose Coupling.
- Separation of Concerns: This principle ensures th...
Architecture
The architectural approach for the recommendation service will leverage a Microservices Architecture combined with Event-Driven Design.
- Microservices: Each microservice will handle dif...
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