Eventual consistency in plain English

Question

I often hear about eventual consistency in different speeches about NoSQL, data grids etc. It seems that definition of eventual consistency varies in many sources (and mayb

Answer 1

When an application makes a change to a data item on one machine, that change has to be propagated to the other replicas. Since the change propagation is not instantaneous, there’s an interval of time during which some of the copies will have the most recent change, but others won’t. In other words, the copies will be mutually inconsistent. However, the change will eventually be propagated to all the copies, and hence the term “eventual consistency”. The term eventual consistency is simply an acknowledgement that there is an unbounded delay in propagating a change made on one machine to all the other copies. Eventual consistency is not meaningful or relevant in centralized (single copy) systems since there’s no need for propagation.

source: http://www.oracle.com/technetwork/products/nosqldb/documentation/consistency-explained-1659908.pdf