CRDTs for Collaborative Apps.

CRDTs (Conflict-free Replicated Data Types) are data structures that automatically merge concurrent edits across devices—ensuring eventual consistency in collaborative apps without needing a central coordinator.

When to use/Use Cases

• Real-time collaborative editors (Google Docs, Figma)
• Shared notes and whiteboards
• Chat apps with offline support
• Geo-distributed data syncing

Example

If Alice types “Hi” offline and Bob adds “!”, a text CRDT ensures both edits merge into “Hi!” once they reconnect.

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Why Is It Important

• Enables low-latency local writes
• Handles network partitions gracefully
• Supports offline-first experiences
• Scales horizontally with distributed replicas

Interview Tips

• Know CRDT types: G-Counter, PN-Counter, OR-Set, LWW-Register, RGA (for text).
• Contrast with Operational Transformation (OT).
• Explain convergence, idempotency, and causality.
• Use a clear example timeline to show how merges happen.

Trade-offs

Pros: offline-first UX, automatic conflict resolution, resilience. Cons: metadata overhead, storage growth (tombstones), eventual—not strict—consistency.

Pitfalls

• Assuming CRDTs guarantee strong consistency
• Overusing last-writer-wins (risk of data loss)
• Ignoring garbage collection of metadata
• Applying CRDTs to global invariants like unique usernames