The CAP Theorem Explained: Balancing the Big Three in Distributed Databases
The CAP theorem, also known as Brewer’s theorem (named after computer scientist Eric Brewer), defines a fundamental trade-off in distributed systems: any distributed data store can provide only two out of three guarantees at any time:
A common phrase used to describe the CAP theorem is: “You can only pick two out of the three.” However, this description is a bit of an oversimplification. Here’s the real crux of the matter:
In the absence of network partitions (meaning the system is fully connected), it is possible to achieve both consistency and availability simultaneously.
In practice, especially for distributed systems that operate over a wide area network (WAN), network partitions are considered inevitable. Systems spread across large geographical distances or across continents are more prone to partitions due to network failures or latency issues.
However, for systems operating within a local network (like a single data center or region), the likelihood of network partitions is significantly reduced. In such cases, a system can often be both consistent and available, since partitioning is rare.
