Weak Consistency (weaker update semantics)
State kept by the replication servers can be weakly consistent. i.e. copies are allowed to diverge temporarily. They will eventually come to agreement.
From time to time, a server picks another server and these two servers exchange updates and converge to the same state.
Total ordering is obtained after getting one message from every server (directly).
Lamport time stamps are used to order messages.
The Anti-Entropy method: Golding 92