Crossreplica

Crossreplica refers to operations, data, or communications that involve more than one replica of a dataset in a distributed system. It describes activities that span multiple copies of the same data maintained for fault tolerance, low latency, or geographic distribution.

In practice, cross-replica work includes reads that access data from more than one replica, writes that update the same data on several replicas, and transactions that require atomicity across replicas.

To maintain consistency across replicas, systems use replication strategies such as synchronous or asynchronous replication and coordination protocols such as Paxos, Raft, or two-phase commit. Anti-entropy processes, including Merkle-tree reconciliations, can repair divergence between replicas in the background. Data versioning with timestamps, vector clocks, or logical clocks supports conflict detection and resolution.

Challenges include the latency and availability costs of coordinating across replicas, especially during network partitions, and conflict resolution when concurrent updates occur. Systems may offer different consistency models, from strong consistency to eventual or causal consistency, selecting a model that matches application requirements.

Use cases include multi-region data stores, disaster recovery setups, and geo-distributed applications that require reads and writes to be served from multiple locations with coordinated updates.

Examples: distributed databases implement cross-replica mechanisms with varying guarantees, from strongly consistent systems to those prioritizing availability and partition tolerance.

See also: distributed databases, replication, and consistency models.