What does "CAP theorem" mean in programming?

Definition

A theorem stating that a distributed system can only guarantee two of three properties simultaneously: Consistency (every read returns the most recent write), Availability (every request receives a response), and Partition tolerance (the system continues working despite network splits). In practice, partition tolerance is required, so the real trade-off is between consistency and availability.

Example

"We chose availability over consistency for the shopping cart — it is more important that users can always add items than that all servers see the same cart at the same instant."

Related terms

• eventual consistency
• sharding
• distributed-systems
• consistency
• availability