Twitter Timeline System Design
System design for Twitter's timeline feed featuring fan-out-on-write architecture, pre-computed timeline caching, and async processing for scalable tweet distribution.
Requirements
Functional
- Users can post tweets with text and media
- Users can follow and unfollow other users
- Users can view their home timeline (tweets from followed users)
- Tweets appear in all followers timelines
Non-Functional
- Timeline loads in <200ms p99 latency
- High availability (99.99% uptime)
- Support 300M+ daily active users
- Tweets are durable once written (zero data loss)
Author
Published
March 11, 2026
Last updated March 11, 2026