Replication gives high availability but causes inconsistencies among replicas. Versioning and vector locks are used to solve inconsistency problems. Versioning means treating each data modification as a new immutable version of data. Before we talk about versioning, let us use an example to explain how inconsistency happens:

As shown in Figure 7, both replica nodes n1 and n2 have the same value. Let us call this value the original value. Server 1 and server 2 get the same value for get(“name”) operation.