Question: Is Redis a database or a cache?

Answer

Redis, which stands for Remote Dictionary Server, is an open-source, in-memory data structure store. It can be used as both a database and a cache, depending on how you configure and use it in your application.

As a Database

When used as a database, Redis stores data in memory with optional durability. This means that it primarily uses RAM to store data, making read and write operations extremely fast. However, it also supports various persistence options, such as AOF (Append Only File) and RDB (Redis Database file snapshots), which allow for data recovery in case of a restart or crash.

A typical usage scenario as a database includes real-time applications like gaming leaderboards, session stores, or real-time analytics, where speed is crucial.

# Example: Storing and retrieving a value in Redis
SET user:1000 '{"name":"John Doe","email":"john@example.com"}'
GET user:1000

As a Cache

When used as a cache, Redis temporarily stores frequently accessed data that is expensive to generate or retrieve, reducing the load on databases or external services and improving application responsiveness. Data stored in Redis as a cache might not be persisted, or it could have an expiration time set using TTLs (Time to Live).

Caching scenarios include caching web page content, session caching, and caching results from database queries or API calls.

# Example: Caching a value with an expiration time
SET product:details:12345 "{\"name\":\"Gadget\",\"price\":99.99}" EX 300 # Cache for 5 minutes (300 seconds)
GET product:details:12345

In summary, Redis's versatility allows it to excel both as an in-memory database and as a caching layer. The choice between using Redis as a database or a cache depends on the needs of your specific application and your requirements regarding data persistence and speed.