Design a swipeable video feed backend
Company: Snapchat
Role: Software Engineer
Category: System Design
Difficulty: medium
Interview Round: Onsite
Design the backend service for a short-video product similar to a “Spotlight”-style feed.
Scope: only the backend “feed vending” functionality that powers the client’s swipe up/down experience.
Functional requirements:
- Client requests a feed and receives an ordered list of video IDs (and minimal metadata) to display.
- Supports endless scrolling/swiping (pagination) with low latency.
- Personalized ranking (can be simplified), plus fallback to non-personalized if needed.
- Avoid showing the same video too often; support “next/previous” navigation.
Non-functional requirements:
- Very high read QPS, low p95 latency.
- Ability to update rankings frequently.
- Basic abuse/spam controls and content eligibility (e.g., blocked creators, geo/age restrictions).
Provide components, APIs, storage, caching, and how you generate and serve ranked results.
Overview: This question evaluates system-design competence for building scalable, low-latency backend services that handle feed vending, pagination, personalized ranking, caching, storage, and content eligibility; it is categorized under System Design and tests practical application of distributed systems and backend data engineering principles.
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