Intermediate LevelSystem Design & Architecture
How do you design a News Feed System (Push/Fan-out on Write vs Pull/Fan-out on Read)?
❓ Interview Prompt: Explain News Feed architecture, Fan-out on Write (Push) vs Fan-out on Read (Pull), hybrid celebrity handling, and feed ranking algorithms.
Designing a social media News Feed System (Facebook/Twitter):
2 Fan-out Strategies:
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Fan-out on Write (Push): When a user posts, the system pushes post IDs directly into every follower's feed cache in Redis. Fast reads ($O(1)$), but fails for celebrities with 50 million followers!
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Fan-out on Read (Pull): Followers fetch posts from followed accounts when opening the app. Fast writes, slow reads.
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Hybrid Approach: Use Fan-out on Write for regular users, and Fan-out on Read for celebrity accounts!
Code Implementation Example
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Hybrid News Feed Fan-Out Architecture:
[User Post] ──> [Fan-Out Worker]
├── (Regular User) ──> Push to Followers' Redis Feed Caches
└── (Celebrity) ──> Save to Celebrity Post DB (Pulled on Read)💡Hybrid Fan-out strategy for social media News Feed systems.
🎯 Interview Key Takeaway
Use a hybrid fan-out model: push posts for regular users to Redis feed caches, and pull posts dynamically for high-follower celebrity accounts.
#System Design#News Feed#Fan-out#Caching#Intermediate
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