How Notion Scaled Its Real-Time Sync Engine

Episode notes

Notion's real-time sync has become table stakes for any collaborative product, but building it was anything but straightforward. In this episode, Lucas and Luna break down how Notion's engineering team moved from a naive polling model to a custom CRDT-based sync engine that handles millions of concurrent edits across documents, databases, and wikis. They walk through the key design decisions: why they chose a hybrid logical clock over vector clocks, how they handle conflict resolution without a central server, and the storage tradeoffs they made to keep latency under 100 milliseconds. Lucas also shares a concrete example of a sync bug that caused data loss for 48 hours in 2021 and how they rebuilt their test harness to prevent it from happening again. If you're building any kind of real-time collaborative app, this episode offers a rare behind-the-scenes look at what it actually takes to make 'instant sync' work at scale.

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