redis

in-memory key-value store, often used as cache, message broker or lightweight database

in-memory: all data lives in RAM, which makes it very fast
not structured
REmote DIctionary Server
use cases:
- caching: fast response for API data, DB queries
- message broker
- simple database (for fast reads/writes)

basic operations

start redis CLI: redis-cli
set a key: SET name "John"
get a key: GET name
increment a key: INCR counter
decrement a key: DECR counter
delete a key: DEL name
set a key with expiration: EXPIRE mykey 10 (expires in 10 seconds)
check if key exists: EXISTS keyname
time to live: TTL keyname
add a value to the beginning of a list: LPUSH tasks "Task1"
add a value to the end of a list: RPUSH tasks "Task1"
return a range of values from a list: LRANGE list_name start_position stop_position
- e.g. print all elements in a list: LRANGE tasks 0 -1
  - 0: first position
  - -1: last position
remove and return the first element: LPOP mylist
remove and return the last element: RPOP mylist
add member(s) to a set: SADD myset "apple" "banana" "cherry"
remove member(s) to a set: SREM myset "apple" "banana" "cherry"
get all members of a set: SMEMBERS myset
check if a value is in a set: SISMEMBER set1 "a"
get all keys that match a pattern: KEYS my* => example output: "myKey", "myCounter", "myExample"
- time complexity O(n)
checks if one or more keys exist: EXISTS myKEY => example output: (integer) 1
- time complexity O(n)

Note

redis doesn't support chaining commands like SET counter 10 INCR counter in a single line each command must be sent separately