What is the CAP theorem?

The CAP theorem states that a distributed system cannot simultaneously guarantee all three properties:

• Consistency: all nodes see the same data at the same time.
• Availability: every request receives a response (successful or error).
• Partition tolerance: the system continues to operate despite network splits.

Due to network partitions, the system must choose between consistency and availability. For example:

• CP systems sacrifice availability for consistency.
• AP systems sacrifice consistency for availability.

This is a fundamental limitation in designing distributed databases and services.