Replication improves the performance and availability of sharing information in a largescale network. Classical, pessimistic replication incurs network access before any access, in order to avoid conflicts and resulting stale reads and lost writes. Pessimistic protocols assume some central locking site or necessitate distributed consensus. The protocols are fragile in the presence of network failures, partitioning, or denial-of-service attacks. They are safe (i.e., stale reads and lost writes do not occur) but at the expense of performance and availability, and they do not scale well.