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.

Preparing for interviews?

Learn core concepts with Grokking System Design Fundamentals, practice patterns in Grokking the Coding Interview, or book Mock Interviews with ex-FAANG engineers for hands-on feedback.

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.