Personalized News Feed Design

System Requirements

• Near real-time generation (1-2 seconds)
• Fast post append (<5 seconds)
• Handle billions of posts
• Personalization at scale

Architecture Components

1. Feed Generation

• User preferences analysis
• Content scoring
• Ranking algorithms

2. Fanout Strategies

Fanout on Write:

• Pre-compute feeds
• Fast reads
• High storage cost

Fanout on Read:

• Compute on demand
• Low storage
• Higher latency

Hybrid Approach:

• Celebrities: Fanout on read
• Regular users: Fanout on write

3. Ranking Model

Features:

• Post recency
• User engagement history
• Social connections
• Content type

4. Storage & Caching

• Redis for hot data
• Database for persistence
• CDN for media

Key Challenges

• Scale (1.66B DAU)
• Personalization
• Real-time updates
• Spam/content quality

News feed systems balance freshness, relevance, and scale.