Let’s look at how some real-world systems exemplify CAP trade-offs:

• MongoDB (CP): MongoDB is a popular NoSQL database which, by default, prioritizes consistency. It uses a primary-secondary replication model. Only the primary can accept writes, and if the primary is lost (partitioned away or down), the system elects a new primary. During that failover window, writes are not accepted – a sacrifice of availability to ensure no two primaries exist (consistency). Once a new primary is in place and secondaries are synchronized, the cluster resumes normal operations