What is CAP Theorem? — UK Software Development Guide
Direct Answer
The CAP Theorem (Brewer's Theorem) states that a distributed data store can provide at most two of three guarantees simultaneously: Consistency (every read receives the most recent write), Availability (every request receives a response — though not necessarily the most recent data), and Partition Tolerance (the system continues to operate despite network partitions — messages between nodes being lost). In practice, since network partitions are inevitable in distributed systems, the real choice is between Consistency and Availability during a partition.
Cap-theorem in the UK
CAP Theorem has direct UK compliance implications. UK GDPR right to erasure requires Consistency: when a user requests deletion of their personal data, all parts of a distributed system must reflect that deletion. An eventually consistent distributed system (choosing Availability and Partition Tolerance) where deletion takes 48 hours to propagate is technically UK GDPR non-compliant unless the Privacy Notice explicitly documents the propagation window. UK FinTech: financial transaction systems must choose Consistency (CP systems) over Availability during network partitions — an unavailable payment system is preferable to inconsistent account balances. NHS clinical data: patient record systems should be CP (consistent, partition tolerant) — a briefly unavailable clinical record is safer than an inconsistent one.
Related Glossary Terms
Cyber Essentials
Cyber Essentials explained for UK software developers and business owners. Cyber Essentials is a UK government-backed cybersecurity certification scheme developed by NCSC (National Cyber Security... UK context, examples, and related services.
DEVOPS
DevOps explained for UK software developers and business owners. DevOps is a set of practices, principles, and culture that combines software development (Dev) and IT operations (Ops) t... UK context, examples, and related services.
Microservices
Microservices explained for UK software developers and business owners. Microservices architecture is a software design approach where an application is built as a collection of small, indepen... UK context, examples, and related services.
Kubernetes
Kubernetes explained for UK software developers. Kubernetes (commonly abbreviated as K8s) is an open-source container orchestration platform that automates the deploymen... UK context and related services.
Docker
Docker explained for UK software developers. Docker is a platform that packages software and its dependencies into standardised units called containers. A Docker con...
Terraform
Terraform explained for UK software developers. Terraform is an open-source Infrastructure as Code (IaC) tool by HashiCorp that allows you to define, provision, and man...
Get Expert Advice on Cap-theorem
Speak with our UK software development experts about Cap-theorem. Free consultation, transparent pricing, no obligation.