# Twitter System Design

Quick Reference: Instagram | Step 7: Pub/Sub

# Quick Reference

Scale: 400M+ tweets/day, 200M+ users

Key Components: Timeline generation, real-time feeds, fan-out, search

Challenges: Real-time timeline generation, write-heavy workload

# Clear Definition

Twitter is a real-time social media platform requiring fast timeline generation, real-time updates, and handling massive write and read volumes.

💡 Key Insight: Twitter uses fan-out (push) for popular users, pull for others. Hybrid approach balances performance and complexity.

# Core Concepts

# Timeline Generation

• Fan-out (Push): Pre-compute timelines for followers
• Pull: Generate on-demand for less active users
• Hybrid: Combine both approaches

# Key Design Decisions

• Sharding: Shard by user_id
• Caching: Cache timelines
• Message Queue: Handle tweet distribution
• Search: Real-time search index

# Quick Reference Summary

Twitter: Real-time social platform with massive scale.

Key Components: Timeline generation, fan-out, search.

Key Design: Hybrid push/pull, sharding, caching.

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