eventuallyconsistent

Eventually consistent is a consistency model used in distributed computing systems. It is a weaker form of consistency compared to strong consistency. In a strongly consistent system, any read operation will return the most recently written value. In contrast, an eventually consistent system guarantees that if no new updates are made to a given data item, all accesses to that item will eventually return the last updated value. However, during the propagation of updates, temporary inconsistencies can occur, meaning different replicas of the data may hold different values for a period of time.

The trade-off for eventual consistency is typically higher availability and performance. Systems that prioritize availability, especially in geographically distributed environments, often adopt eventual consistency. This is because achieving strong consistency across all nodes in a distributed system can be complex and lead to performance bottlenecks and reduced availability, particularly in the face of network partitions or node failures.

Examples of systems that employ eventual consistency include many NoSQL databases like Amazon DynamoDB, Cassandra, and the DNS (Domain Name System). These systems often use techniques such as read repair and write repair to help reconcile inconsistencies over time. When a write operation occurs, it is propagated to a subset of nodes. Subsequent reads may hit a node that has not yet received the update, leading to a stale read. However, the system is designed such that eventually, all nodes will converge to the same state. Applications using eventually consistent systems must be designed to tolerate reading stale data and handle potential conflicts arising from concurrent updates to the same data item.