The problem
Notion’s existing collaboration layer was hitting latency walls as the document base grew past 10 million. Concurrent editing introduced merge conflicts, and users in different regions experienced noticeable lag. The team needed a new sync engine that could scale horizontally without sacrificing real-time feel.
Our approach
We worked alongside Notion’s core infrastructure team over six months. We designed a CRDT-based sync engine that could handle concurrent edits without server-side conflict resolution. The system was built to be region-aware, routing sync traffic through the nearest edge node. We also built a comprehensive testing harness that simulated 10,000 concurrent editors to validate latency under load.
Results
Sync latency dropped below 100ms for 99th percentile users, even across continents. The new engine handled 3x the concurrent editor load with half the infrastructure cost. Document merge conflicts were eliminated entirely through the CRDT approach.