Living Reference Work Entry

Encyclopedia of Database Systems

pp 1-2

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Eventual Consistency

  • Marc ShapiroAffiliated withUPMC-LIP6 & INRIA Paris Email author 
  • , Bettina KemmeAffiliated withSchool of Computer Science, McGill University


Lazy replication; Optimistic replication


In a replicated database, the consistency level defines whether and how the values of the replicas of a logical object may diverge in the presence of updates. Eventual consistency is the weakest consistency level that guarantees convergence. Informally, it requires that all replicas of an object will eventually reach the same final value, assuming that no new updates are submitted to the object.

Formal Definition and Usage

Eventual consistency is an important correctness criteria in systems with a lazy, update-anywhere strategy, also referred to as optimistic replication. Update operations can be submitted and executed on any node, and the propagation of updates occurs lazily after they are committed. Conflict resolution and reconciliation must ensure that all replicas (copies) of a logical object eventually converge to the same value. Different objects are considered independent. Especially in wide-area settings, also referred to ...

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