Relaxed concurrency control (RCC) is a technique used in distributed databases to balance consistency
and performance by allowing some level of inconsistency in exchange for improved performance and
scalability. Unlike traditional strict concurrency control methods, which enforce strong consistency
guarantees, RCC provides a more flexible approach that can be tailored to the specific needs of an
application.
Use Cases
i. Social Media Platforms: In social media applications, it is often acceptable to have slight inconsistencies
in the data (e.g., the number of likes on a post) as long as the system remains highly responsive and can
handle a large number of concurrent users.
ii. E-commerce Websites: For e-commerce platforms, ensuring that inventory levels are accurate is
important, but slight delays in updating inventory across distributed nodes can be tolerated to maintain
high performance and user experience.
iii. Content Delivery Networks (CDNs): CDNs prioritize delivering content quickly to users. RCC allows for
slight inconsistencies in cached content across different nodes, which can be acceptable in exchange for
faster content delivery.
Balancing Consistency and Performance
i. Eventual Consistency: RCC often employs the concept of eventual consistency, where the system
guarantees that, given enough time, all replicas will converge to the same state. This allows for
temporary inconsistencies while ensuring long-term data integrity.
ii. Conflict Resolution: RCC systems use various conflict resolution strategies to handle inconsistencies. For
example, they might use version vectors, timestamps, or application-specific rules to resolve conflicts
when data is updated concurrently.
iii. Partition Tolerance: RCC is designed to handle network partitions gracefully. During a partition, different
parts of the system may operate independently, and once the partition is resolved, the system reconciles
any inconsistencies.
iv. Latency Reduction: By relaxing strict consistency requirements, RCC reduces the need for synchronous
communication between distributed nodes, thereby reducing latency and improving overall system
performance.
v. Scalability: RCC allows distributed databases to scale more effectively by reducing the overhead
associated with maintaining strict consistency. This makes it easier to add new nodes and handle
increased workloads.
Hence, relaxed concurrency control (RCC) improves performance and scalability by allowing temporary inconsistencies, making it ideal for systems like social media and e-commerce.