CAP vs. PACELC Theorem in Distributed Systems

CAP describes an impossibility during a network partition. PACELC adds a way to discuss the latency cost of consistency during normal operation. This lesson works through a two-replica example and shows why a database name alone is not enough to identify its guarantees.

When designing systems that span multiple servers or data centers, how do we ensure they remain reliable and performant?

This question is fundamental to System Design. Building these systems means constantly managing trade-offs. We need to manage communication across multiple nodes, handle inevitable network failures, and maintain data consistency, all while delivering a fast and seamless user experience.

Frameworks like the CAP and PACELC theorems provide a mental model for navigating these complexities.

They do not give us the answers, but they help us ask the right questions about the trade-offs we must make. We’ll discuss both of these frameworks in detail in this lesson. Let’s start by understanding the inherent trade-offs in distributed systems.

Balancing trade-offs in distributed systems

Building distributed systems involves orchestrating multiple computers to work together as a cohesive unit.