The CAP theorem, also known as Brewer’s theorem, states that in a distributed system, it is impossible to simultaneously provide consistency, availability, and partition tolerance (CAP). Consistency means that all nodes in the system see the same data at the same time, availability means that every request gets a response, and partition tolerance means that the system continues to operate despite network partitions. In other words, you can only choose two out of these three guarantees, and you have to give up the third.
On the other hand, the BASE properties (Basically Available, Soft state, Eventual consistency) provide an alternative approach to building distributed systems that prioritize availability and partition tolerance at the expense of strong consistency.
Basically Available means that the system will always be available to provide a response, even if the response is not the most recent or accurate. Soft state means that the state of the system can change over time, even without any input. Eventual consistency means that the system will become consistent at some point in the future, but not necessarily immediately.
The BASE properties provide a useful approach to building distributed systems that prioritize availability over consistency. This is because in a distributed system, network partitions are likely to occur, and it is important that the system remains available in such situations. In contrast, maintaining strong consistency in the face of network partitions can be challenging and may require significant overhead.
To give an example, let us consider a distributed e-commerce application where users can place orders. In a strongly consistent system, all nodes would have to agree on the order being placed before it can be confirmed to the user. This can be problematic if there is a partition in the network, as some nodes may not be able to communicate with others and the system will become unavailable. In contrast, a system that prioritizes availability over consistency may allow the user to place the order even if there is a partition. This would increase the availability of the system, at the expense of consistency.
In summary, the CAP theorem and the BASE properties present two different approaches to building distributed systems. The CAP theorem prioritizes consistency over availability, while BASE properties prioritize availability over consistency. It is important to carefully consider which approach is most appropriate for the specific requirements of a given system.