Introduction

Redis is an in-memory data store: it keeps data in RAM instead of on disk, which makes it roughly a hundred times faster than a disk database for simple operations — but also means it is not where your permanent data should live alone. Redis is the accelerator you bolt onto a real database, and it powers caching, sessions, leaderboards, and queues across the modern web.

Caching: the job Redis is famous for

The most common Redis job is caching: storing the result of an expensive database query so the next request doesn't repeat it.

User requests homepage → Check Redis for "homepage:en" → Found? Return it instantly (milliseconds) → Not found? Query Postgres, store the result in Redis with a 60-second expiry, return it

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Expiry is the key idea: cached data gets a time-to-live ( TTL ), after which Redis deletes it and the next request refreshes it from the real database.…