“CA” stands for Consistency and Availability, in the context of the CAP (Consistency, Availability, Partition tolerance) theorem. A CA System delivers consistency and availability across all the nodes. It can’t do this if there is a partition between any two nodes in the system and therefore does’t support partition tolerance.
What is Consistency?
In a system that guarantees consistency, all nodes in the system have the same data at the same time. When a write operation is completed, all subsequent read operations will return the updated value. This ensures that clients always see a consistent view of the data.
What is Availability?
In a system that guarantees availability, every request receives a response, even if some nodes in the system are experiencing failures or network issues. The system remains operational and responsive to client requests.
What is the CA Trade-Off?
Let’s consider what happens when there is a network partition (P) between two nodes in the system.
- If a network partition occurs, it means that the two sets of nodes on either side of the partition cannot communicate with each other.
- In this scenario, ensuring Consistency (C) across all nodes becomes impossible because the nodes on each side of the partition cannot synchronize their data.
- As a result, the system must choose between maintaining Consistency (C) or Availability (A).
- Since a CA system prioritizes both Consistency (C) and Availability (A), it cannot sacrifice either property in the presence of a network partition.
Therefore, a CA system cannot support Partition tolerance (P), which means it cannot guarantee that the system will continue to operate correctly despite network partitions. This trade-off is at the core of the CAP theorem, which states that a distributed system can only achieve two out of the three properties (Consistency, Availability, and Partition tolerance) at any given time.
Use Cases of CA Systems
Below are the Use Cases of CA Systems
- Financial Transactions: Systems processing financial transactions require strong consistency to ensure accuracy and integrity. High availability is also crucial to maintain operations during peak times.
- E-commerce Platforms: E-commerce sites need consistent product information, pricing, and inventory levels. They also require high availability to handle traffic spikes and ensure seamless shopping experiences.
- Healthcare Systems: Healthcare systems storing patient records and medical data need strong consistency for accuracy and availability to ensure patient care is not interrupted.
- Government Systems: Government systems managing citizen data and public services require strong consistency for data accuracy and high availability for uninterrupted access to critical services.