Question

In the context of the CAP theorem, what happens to a distributed system if it chooses to remain available during a network partition?

Accepted Answer

The CAP theorem states that a distributed system can only provide two of three guarantees simultaneously: Consistency, Availability, and Partition Tolerance. A network partition occurs when communication between nodes in a system is interrupted, causing the system to split into isolated groups that cannot send messages to each other. If a system chooses to remain available during a partition, it prioritizes Availability over Consistency. This means that even though the nodes cannot synchronize data because of the communication failure, the system continues to accept read and write requests from clients. Because the nodes cannot update each other, the system accepts the risk that different users may receive different, outdated, or conflicting versions of the data. For example, if a user updates their profile information on one side of a partitioned network, a user on the other side of the partition will not see that update and will continue to read the old data. Consequently, the system sacrifices data consistency, meaning it can no longer guarantee that every read operation receives the most recent write or the same data across all nodes, in exchange for remaining functional and responsive to users during the network outage.

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In the context of the CAP theorem, what happens to a distributed system if it chooses to remain available during a network partition?