Delta consistency is one of the consistency model

Consistency model

In computer science, consistency models are used in distributed systems like distributed shared memory systems or distributed data stores . The system supports a given model, if operations on memory follow specific rules...

s used in the domain of parallel programming, for example in distributed shared memory

Distributed shared memory

Distributed Shared Memory , in Computer Architecture is a form of memory architecture where the memories can be addressed as one address space...

, distributed transactions, and Optimistic replication

Optimistic replication

Optimistic replication is a strategy for replication in which replicas are allowed to diverge.Traditional pessimistic replication systems try to guarantee from the beginning that all of the replicas are identical to each other, as if there was only a single copy of the data all along...

The delta consistency model states that an update will propagate through the system and all replicas will be consistent after a fixed time period δ. In other words, the result of any read operation is consistent with a read on the original copy of an
object except for a (short) bounded interval after a modification. So basically, if you have an object which is modified, during the short period of time following its modification, the read will not be consistent. Then, after a fixed time period, the modification is propagated and the read will be consistent.

Sources

• Communication Systems: The State of the Art : IFIP 17th World Computer Congress, Lyman Chapin ed. 2002