The CAP Theorem Question Every Senior System Design Interview Asks

The CAP theorem is often misunderstood in system design interviews, where the interviewer is actually looking for the PACELC framework. The CAP theorem states that a distributed system cannot guarantee consistency, availability, and partition tolerance simultaneously, but it doesn't address what happens during normal operation. The PACELC framework, on the other hand, considers two axes: partition behavior and steady-state behavior, with four possible tradeoffs. Interviewers often test candidates' understanding of these tradeoffs, particularly in the PA/EL, PA/EC, PC/EL, and PC/EC corners of the matrix.