CRDTs — Notes

When you actually need them

• Offline-first apps that sync later.
• Multi-leader / multi-region writes without a coordinator.
• Collaborative editors (Docs, Figma, Notion, whiteboards).
• Mobile sync (CouchDB / Couchbase Lite).
• Edge clouds (Cloudflare Durable Objects, Cloudflare D1 alt).

CRDT vs OT (Operational Transformation)

• OT transforms incoming ops against local concurrent ops; requires server with global order (Google Docs original).
• CRDTs decentralize but at higher memory / metadata cost.
• Modern collab tools (Yjs, Automerge) use CRDTs; Google Docs / Quill moved partially.

Practical concerns

• Garbage collection: tombstones and old version metadata must be GC'd once all replicas have observed them — needs causal stability tracking.
• Bandwidth: state-based diffing is hard; delta-CRDTs ship only deltas.
• Permissions / ACL: CRDTs don't model authorization; layer on top.

Where they show up in this repo

• Google Docs, Figma, Notion, Online Whiteboard, Collab editor.
• Distributed cache (counters), shopping cart (Dynamo).
• Multi-region key-value stores (Riak, Redis Enterprise).

Refs

• Shapiro, Preguiça et al.: "Conflict-free Replicated Data Types" (SSS '11).
• Almeida et al.: "Delta-CRDTs."
• Yjs / Automerge papers and docs.
• Riak DT docs; Akka Distributed Data; Cassandra LWW limits.