CRDTs & Conflict Resolution

Why CRDTs

In distributed systems, updates can arrive out of order. Conflict-free Replicated Data Types (CRDTs) guarantee convergence without coordination.

Key idea

A CRDT defines a merge function that is:

• Commutative (A ⊔ B = B ⊔ A)
• Associative (A ⊔ (B ⊔ C) = (A ⊔ B) ⊔ C)
• Idempotent (A ⊔ A = A)

These properties ensure replicas converge even with duplicated or reordered updates.

What you will build

• G-Counter merge (grow-only counter)
• LWW Register merge (last-write-wins)
• PN-Counter merge (inc/dec)
• OR-Set merge (observed-remove set)
• MV-Register merge (concurrent values)