Living Reference Work Entry

Encyclopedia of Database Systems

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Optimistic Replication and Resolution

Synonyms

Asynchronous Replication; Lazy replication; Optimistic replication; Reconciliation-based data replication

The term “optimistic replication” is prevalent in the distributed systems and distributed algorithms literature. The database literature prefers “lazy replication.”

Definition

Data replication places physical copies of a shared logical item onto different sites. Optimistic replication (OR) [17] allows a program at some site to read or update the local replica at any time. An update is tentative because it may conflict with a remote update. Such conflicts are resolved after the fact, in the background. Replicas may diverge occasionally but are expected to converge eventually (see “Eventual Consistency”).

OR avoids the need for distributed coordination prior to using an item. It allows a site to execute even when remote sites have crashed, when network connectivity is poor or expensive, or while disconnected from the network.

The defining characteristic of OR is that any communica ...

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