I knew this type of question was coming and still managed to fumble the structure.
Start by clarifying requirements and scale (e.g., 1B users, 100M daily posts), then design the core data model and high-level architecture. Focus on the feed generation strategy (fan-out on write vs. read) and how to handle likes/comments at scale, discussing trade-offs and bottlenecks.
Pro tip: Proactively discuss the trade-offs between fan-out on write and fan-out on read, and propose a hybrid approach for celebrities. This shows you understand real-world constraints and can make pragmatic decisions.
Ask about functional requirements (posting, feed, likes, comments) and non-functional requirements (latency, availability, consistency). Estimate scale: number of users, posts per day, read/write ratio.
Sketch the main components: clients, API gateway, services (user, post, feed, like, comment), databases (SQL/NoSQL), cache, message queue, and CDN for media. Explain data flow for posting and viewing feed.
Define schemas for users, posts, follows, likes, comments. Choose appropriate databases: e.g., graph DB for social graph, wide-column for posts, and caching for hot data. Discuss sharding and replication.
Explain feed generation: fan-out on write vs. read, and hybrid approach. Discuss ranking algorithm (e.g., chronological vs. algorithmic) and how to handle celebrities. Mention caching and precomputation.
Address bottlenecks: hot keys, thundering herd, consistency vs. availability. Discuss trade-offs in like/comment counts (eventual consistency), media storage (CDN), and real-time updates (WebSockets vs. polling).
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.