Redis: The Basics

What is Redis ?
- Redis is an open source (BSD licensed), in-memory data structure store, used as database, cache and message broker
- Remote Dictionary Server

Installation

For Mac OS X:
1. Install XCode Developer Tools
2. Download the stable release on Redis official site: http://redis.io/download
3. Run the ff. command:

wget http://download.redis.io/releases/redis-3.2.0.tar.gz
tar xzf redis-3.2.0.tar.gz
cd redis-3.2.0

# install and run globally (/usr/local/bin)
make install
redis-server

# install and run locally
make
cd src && ./redis-server

# install on another location
make install /opt/local/bin

For Ubuntu:
1. Run the ff. command:

sudo apt-get install redis-server

# run
redis-server

Data Types

List:
- collection of string elements, sorted according to the order of insertion. ex. 8, 9, 1, 2, 3
- implemented using a linked list, not using an array
- insertion of new elements to head or tail is at constant time regardless of the length of the list

Disadvantage:
- getting element by specific index is an extremely slow operation compared to list implemented using array

Advantage:
- can add elements to a very long list in a very fast way
- a list can be retrived at constant length in constant time

Common use cases for Lists
- Remember the latest updates posted by users into a social network.

Capped Lists
- List can be capped to only remember the latest N items and discard the old items

RPUSH - insert element in the tail of the list

127.0.0.1:6379> RPUSH char "B" "C"
(integer) 2
127.0.0.1:6379> LRANGE char 0 -1
1) "B"
2) "C"

LPUSH - insert element in the head of the list

127.0.0.1:6379> LPUSH char "A"
(integer) 3
127.0.0.1:6379> LRANGE char 0 -1
1) "A"
2) "B"
3) "C"

LRANGE - gives a subset of the list

127.0.0.1:6379> LRANGE char 0 1
1) "A"
2) "B"

LLEN - returns the current length of the list

127.0.0.1:6379> LLEN char
(integer) 3

LPOP - removes element from the start of the list and returns it

127.0.0.1:6379> LPOP char
"A"

RPOP - removes element from the start of the list and returns it

127.0.0.1:6379> RPOP char
"C"

Sets:
- similar to List except elements are not in order and must be unique

SADD - adds given value to a set

127.0.0.1:6379> SADD family "Jane" "John" "Paul" "Rachel"
(integer) 4
127.0.0.1:6379> SADD friends "Anna" "John" "Dave"
(integer) 3

SREM - removes given value from a set

127.0.0.1:6379> SREM family "Paul"
(integer) 1

SMEMBERS - returns list of all the members in a set

127.0.0.1:6379> SMEMBERS family
1) "John"
2) "Rachel"
3) "Jane"

SISMEMBER - tests if a given value is in the set

127.0.0.1:6379> SISMEMBER family "Paul"
(integer) 0

SUNION - combines two or more sets and returns the list of all elements.

 # combine family and friends
127.0.0.1:6379> SUNION family friends
1) "Anna"
2) "John"
3) "Rachel"
4) "Jane"
5) "Dave"

SINTER - Returns the members of the set resulting from the intersection of all the given sets.

 # getting the common friend and family
127.0.0.1:6379> SINTER family friends
1) "John"

Sorted Sets:
- similar to Set but strings are defined by score, which allows the retrieval of elements in an ordered list
- score provides sorting and ranking capabilities

Common use cases for Sorted Sets
- leaderboard system

ZADD - adds all the specified members with the specified scores to the sorted set stored at key

127.0.0.1:6379> ZADD grades 75 John 72 Maine 77 Michael 80 Abby 83 Becky 87 Dave 81 Elsa 84 Ginny 89 Ivan
(integer) 9

You can also add score and members individually:

127.0.0.1:6379> ZADD users 1989 Jasmin
(integer) 1
127.0.0.1:6379> ZADD users 1970 Camille
(integer) 1
127.0.0.1:6379> ZADD users 1993 Jessica
(integer) 1
127.0.0.1:6379> ZADD users 1985 Tiffany
(integer) 1

ZRANGE - returns the specified range of elements in the sorted set stored at key.

127.0.0.1:6379> ZRANGE users 0 -1
1) "Camille"
2) "Tiffany"
3) "Jasmin"
4) "Jessica"

ZCOUNT - returns the number of elements in the sorted set at key with a score between min and max

 # counting students with grades between 80 and 90
127.0.0.1:6379> ZCOUNT grades 80 90
(integer) 6

ZREVRANK - returns the rank of member in the sorted set stored at key, with the scores ordered from high to low

 # getting the rank of Becky from highest to lowest grade
127.0.0.1:6379> ZREVRANK grades Becky
(integer) 3

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

HSET - Sets field in the hash stored at key to value.

127.0.0.1:6379> HSET user:jane name Jane
(integer) 1

HGET - Returns the value associated with field in the hash stored at key.

127.0.0.1:6379> HGET user:jane name
"Jane"

HMSET - Sets the specified fields to their respective values in the hash stored at key.

127.0.0.1:6379> HMSET user:jane email "jane@gmail.com" hometown Laguna gender Female
OK

HMGET - Returns the values associated with the specified fields in the hash stored at key.

127.0.0.1:6379> HMGET user:jane name email
1) "Jane"
2) "jane@gmail.com"

HGETALL - Returns all fields and values of the hash stored at key.

127.0.0.1:6379> HGETALL user:jane
1) "name"
2) "Jane"
3) "email"
4) "jane@gmail.com"
5) "hometown"
6) "Laguna"
7) "gender"
8) "Female"