Optimizing Facebook for iOS start time
Article Summary
Meta's iOS team achieved multi-second improvements in Facebook app startup by rethinking when work actually needs to happen.
The Facebook iOS engineering team tackled one of mobile's most critical metrics: cold start time. They measured from icon tap to feed loaded, matching actual user perception rather than arbitrary technical milestones.
Key Takeaways
- Reduced feed request dependencies to just auth and cursors for parallel initialization
- UDP Priming sends encrypted feed requests before TCP connection completes
- Switched from batch fetching (3+7 stories) to streaming (1+1+X) for faster response
- Deferred noncritical services with queuing until startup completion
- Delivered multi-second improvement in perceived startup time
Critical Insight
By decoupling dependencies, leveraging UDP priming, and deferring non-critical work, Meta cut Facebook iOS cold start time by multiple seconds.
