Playing with Redis

A couple of weeks ago, I went to a Redis Meetup in Lille, presented by François Cerbelle. It motivated me to look a bit more into Redis.

Redis is an open-source in-memory key-value database, which supports different kinds of data structures, such as strings, lists, maps, sets, sorted sets…

Or as said on the official website:

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.

Interactive tutorial

An interactive tutorial is available at, which presents the basic but most important features of Redis.

Basic CLI commands

set my_key my_value => returns OK
get my_key => return my_value

Atomic operations

set my_counter 1 => returns OK
incr my_counter => returns 2, set my_counter to 2 atomically
decr my_counter => returns 1, set my_counter to 1 atomically
  • Handle expiration
set resource:lock "redis lock"
expire resource:lock 120 => the key resource:lock will be deleted in 120 seconds
ttl resource:lock => returns the number of seconds before expiration (eg. 111)

ttl will return -2 if the resource has expired, -1 if the resource will never expire, or a positive number for the remaining seconds before expiration.

  • Lists
rpush my_list my_val1 => puts my_val1 at the end of my_list, returns the size of the list
lpush my_list my_val2 => puts my_val2 at the beginning of my_list, returns the size of the list
lrange my_list 1 4 => returns the elements from index 1 to index 4 (0-based)
llen my_list => returns the size of the list
lpop my_list => removes the first element of the list and returns it
rpop my_list -> removes the last element of the list and returns it
  • Sets
sadd my_set my_val1 => add my_val1 to the set, returns the number of values added (if my_set already contains my_val1, will return 0)
srem my_set my_val2 => remove my_val2 from the set, returns the number of values removed (if my_set doesn't contain my_val2, will return 0)
sismember my_set my_val1 => returns 1 if my_set contains my_val1, 0 otherwise
smembers my_set => returns the members of the set
sunion my_set1 my_set2 => returns the combined members of my_set1 and my_set2
  • Sorted sets
zadd my_sorted_set 1.5 my_val1 => add my_val1 to my_sorted_set with the weight 1.5, returns the number of values added
zadd my_sorted_set 1.2 my_val2 => add my_val2 to my_sorted_set with the weight 1.2
zrange my_sorted_set 0 1
  • Hashes

Hashes are maps between string fields and string values, so they are the perfect data type to represent objects

hset user:1000 name "user name"
hset user:1000 email "user email"
hset user:1000 password "user password"
hgetall user:1000 => returns all the saved data 
hmset user:1001 name "user name 2" password "hidden" email "user password 2"
hget user:1001 name => "user name 2"

Atomic operations on hashes

hset user:1000 visits 10
hincrby user:1000 visits 1 => 11
hincrby user:1000 visits 10 => 21
hdel user:1000 visits
hincrby user:1000 visits 1 => 1

Running with Docker

You can use the official Docker image for Redis:

docker run --name some-redis -d redis:4

An Alpine version is available:

docker run --name some-redis -d redis:4-alpine

Run with your own configuration

You can create (or modify) a redis.conf file for your configuration. A corresponding Dockerfile would be:

FROM redis:4-alpine
COPY redis.conf /usr/local/etc/redis/redis.conf
CMD [ "redis-server", "/usr/local/etc/redis/redis.conf" ]

If you want to test the CLI operations described here, you can run a redis-cli client :

docker run -it --rm redis:4-alpine redis-cli -h some-redis -p 6379