Design a Ad Serving Service
Last updated: February 9, 2026
Quick Overview
Design a low-latency ad serving system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Notion
February 9, 202640
4
219 solved
Design a low-latency ad serving system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Software engineering fundamentals questions at Notion test your understanding of core CS concepts and their practical application. This System Design Round question evaluates how you apply engineering principles to build maintainable, scalable software.
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
- What testing strategy would you use for this component?
- What are the security implications of this design?
- How would you document this for other engineers?
- How would you handle backward compatibility?
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Core Design Principles
For the Ad Serving Service, the primary design principles that apply are Separation of Concerns and Scalability.
- Separation of Concerns ensures that different components of the system...
Architecture
The architecture for the Ad Serving Service at Notion will adopt a Microservices Architecture.
- Ad Selection Service: Responsible for selecting the right ads based on user data and prefere...
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