CONCEPT Cited by 1 source
Last-write-wins¶
What it is¶
Last-write-wins (LWW) is a conflict-resolution rule for concurrent updates to the same state: if two replicas update the same field, the one with the later timestamp wins.
The timestamp flavour matters:
- Wall-clock LWW — uses real-world time. Sensitive to clock skew; can lose correct writes from a node whose clock drifts slightly behind.
- Logical-clock LWW (Lamport / vector / hybrid-logical clocks) — uses a per-node monotonic counter that increments on every event and advances when receiving a higher counter from another node. Resolves causal ordering without depending on wall-clock sync.
Why LWW over consensus¶
LWW lets you accept writes at any replica without coordination and still converge deterministically. It's the workhorse conflict-resolution rule for CRDT-backed gossip systems and eventually-consistent stores.
Trade-off: the "loser" write is silently overwritten. In shapes where writes rarely actually conflict (one writer per key), LWW is effectively free. In shapes with hot contention, it silently drops data — picks for this case are application specific (CRDTs, CmRDTs, OT, or consensus).
Canonical wiki instance — cr-sqlite / Corrosion¶
cr-sqlite resolves row-level CRDT merges via LWW using logical timestamps:
"Updates to tables are applied last-write-wins using logical timestamps (that is, causal ordering rather than wall-clock ordering)." — sources/2025-10-22-flyio-corrosion
The shape works at Fly.io because their orchestration model makes workers the source of truth for their own Machines — conflicts between workers are rare by construction.
Seen in¶
- sources/2025-10-22-flyio-corrosion — canonical primary source disclosing cr-sqlite's causal-LWW rule for Corrosion.