lastwritewins

Last-write-wins, often abbreviated LWW, is a conflict resolution strategy used in distributed systems and eventually consistent data stores. When multiple replicas concurrently update the same item, the update with the most recent timestamp is treated as authoritative and overwrites earlier versions.

Implementation relies on each write being tagged with a timestamp, typically generated by the client or server. During reconciliation, replicas compare timestamps and apply the value with the largest one. If two writes share the same timestamp, a deterministic tie-breaker such as the source node identifier or a sequence number is used to ensure a single outcome.

The approach is simple and fast, offering straightforward conflict resolution and low coordination overhead. It is well-suited for latency-sensitive workloads and scenarios where recent updates should prevail. However, LWW depends on reasonably synchronized clocks; clock skew, drift, or clock manipulation can lead to inconsistent or unintuitive results. It can also cause older, potentially valid updates to be lost when newer writes arrive late, and it does not provide strong consistency guarantees or full historical auditability.

LWW is commonly used in Dynamo-style key-value stores and in some Cassandra configurations, where conflict resolution is performed by choosing the value with the latest timestamp. In CRDT terminology, LWW appears in constructs such as LWW-Register and LWW-Set, which use timestamps to decide membership or value.

Overall, last-write-wins is a pragmatic trade-off, favoring speed and simplicity over strict consistency and historical preservation.