What is Redis?

Redis is an in-memory database used for very fast data storage and access.

Its name stands for REmote DIctionary Server.

#The main idea

Redis stores data in RAM, not on disk, so it runs tens of times faster than ordinary databases (e.g. PostgreSQL or MySQL).

#Data types

Redis isn't just "key-value". It supports several structures:

• strings, plain values;
• lists, ordered collections;
• sets, unique elements;
• hashes, fields and values (like a dictionary);
• sorted sets, with priorities (rankings, leaderboards);
• streams, bitmaps, geospatial data, and more.

#How it works

• All data is stored in RAM, but Redis can periodically save it to disk (a snapshot) or to a log (AOF), so nothing is lost on a failure.
• Access follows the key → value principle.

#Main uses

• Caching (speeding up web services).
• Storing user sessions.
• Message queues and pub/sub systems.
• Counters, rankings, timers (thanks to atomic operations).

#Characteristics

• Very high speed (operations take milliseconds).
• Supports TTL, a key's time to live (it's removed automatically).
• Can run as a cluster for scaling.

Summary: Redis is an extremely fast in-memory database, a great fit for caches, queues, and real-time systems, where access speed matters more than complex relationships.