Introduction

1. What This Module Covers

The storage module ended with an observation: a cache is a small, short-lived read model. This module takes that observation seriously, because the cache is the most used and most misused piece of infrastructure in the industry, and the one interviewers ask about most.

The idea itself is simple: keep the things you use often somewhere fast. A cache is a small, fast copy of data whose real home is somewhere slower, and one number decides whether yours is any good: the hit ratio, the fraction of lookups that find the data. The math is strict