Consistency - The result of a read at T1 is the same as T2 if there were no writes between T1 and T2. Basically, any read can see any previously completed write.
Wikipedia defines Consistency as all nodes see the same data at the same time, but that is incorrect because the CAP Theorem is defined in terms of the observed rather than actual state of the system. |
Optimistic availability is a characteristic of distributed systems that are coordinated by a master node which allows the system to tolerate arbitrary node failure while preserving availability as long as the master node and at least one relevant node agree on the state of the system. In laymen's terms: given sufficient replication, if a node fails, we're optimistic that the system will remain available.