Christian Engvall

What is Redis and what is it used for? I’ve come across it in two of the projects I’ve been working on, but never had to do anything else than start it. It seems to be used along side a persistence database.

This is the first post in the What is series where I’m aiming to answer questions I’m thinking about but never take the time to answer. I got this idea from another Swedish developer, who I cant remember the name of right now. Inez or Ines maybe? If you know who i’m looking for, please let me know in the comments :)

How does redis explain itself

Redis is an open source (BSD licensed), in-memory data structure store, used as a database, cache and message broker. It supports data structures such as strings, hashes, lists, sets, sorted sets with range queries, bitmaps, hyperloglogs and geospatial indexes with radius queries. Redis has built-in replication, Lua scripting, LRU eviction, transactions and different levels of on-disk persistence, and provides high availability via Redis Sentinel and automatic partitioning with Redis Cluster. -Redis.io

Ok, so I guess it can be used as a database itself, and i do not need to have another one in my application, such as postgres, mysql or any other database.

It seems to be some kind of cache as well. Have to look into that.

Is it a cache, database or both?

After going through the FAQ I learned that using Redis together with an on-disk database is a good idea and a common design pattern that is used. Use Redis for write heavy small data and store big blobs of data into an sql on disk database.

But you can use redis as a stand alone database that keeps data in memory and eventually saves it to disk.

But what do they mean by using it as a cache? Well, since Redis keeps data in memory you can load data into it that is used and displayed often without getting the data from disk everytime, for example loading product data from an sql-database, making it very quick.

Installing redis

I used this guide to install Redis.

brew install redis

And then when it’s installed i ran this command to launch Redis when my computer starts.

ln -sfv /usr/local/opt/redis/*.plist ~/Library/LaunchAgents

To check if redis is running you can run:

redis-cli ping

This should reply pong if it’s running, else it says

Could not connect to Redis at 127.0.0.1:6379: Connection refused

Then you need to run this command in a terminal to start it:

redis-server