Making Direct Messages Reliable and Fast
Article Summary
Instagram DMs handle millions of messages per second. How do they make every send feel instant, even when your network drops mid-tap?
Instagram's engineering team built a centralized Mutation Manager to solve two critical problems: making network requests feel instantaneous and ensuring messages never get lost, even across app crashes. This deep dive reveals the architecture behind reliable, fast messaging at scale.
Key Takeaways
- Optimistic state updates UI instantly before server confirms, eliminating perceived latency
- Mutation Manager serializes requests to disk for automatic retry across crashes
- Separate optimistic and server data caches prevent clobbering and inconsistent UI states
- Message ordering preserved automatically through centralized mutation queue
- Debug logs track every request attempt with timestamps and error codes
Critical Insight
By separating optimistic state from server data and centralizing mutation logic, Instagram made DMs feel instant while guaranteeing delivery reliability across all network conditions.
