Redis datatypes

Documentation

commands (note filter by datatype)

https://redis.io/commands

Keys

• keys are binary safe (safe to use string, or contents of a jpg)
• keys are unique, should be long enough to be descriptive, but not so long to inflate lookup cost
• keys are automatically added by set/rpush/... operations if key does not yet exist
• keys are automatically deleted when they do not hold a value
• you cannot get/set a key at the same time, making it possible to use redis as a queue
• you can assign a TTL on keys

Strings

https://redis.io/commands#string

• strings are binary safe (may contain binary blobs)
• strings can have a size up to 512MB

SET key value         # a string
SET key 100           # still a string

SETBIT foo 2 f        # set key 'foo's 2nd character to 'f'  
SETNX foo 1           # set key 'foo' if not exists
MSET key-1 1 key-2 2  # set multiple keys at once
INCR key              # increments string as if were number

Collections

Lists

https://redis.io/commands#list

• retrieving items is O(n)
• lists are 0-indexed
• lists support negative indexes (starting from tail of list)
• popping items from an empty list returns (nil).
• lists can support very large numbers of items, queues for example often refer to a single key, continuously pushing items to the end of the list.

RPUSH key 1  # append '1' to list (returns index) (creates if not exist)
LPUSH key 1  # prepend '1' to list (returns index) (creates if not exist)

LPOP key     # remove/return first item in list
RPOP key     # remove/return last item in list

BLPOP key 5  # remove/return first item in list (wait up to 5s before returning if empty -- more efficient polling)
BRPOP key 5  # remove/return last item in lest (wait up to 5s before returning if empty -- more efficient polling)

LRANGE 0 -1  # list all elements in list
LTRIM  0  2  # return first 2x items in list, and remove all other items from it

Sets

https://redis.io/commands#set

• retrieving items is O(1) -> O(n)
• all members are strings

SADD key 1 2 3   # add elements to set

SMEMBERS key     # print all members of set
SISMEMBER key 2  # test if '2' is member of set
SPOP             # return random element

Sorted Sets

A set that is sorted by a score string.

#       {score}  {value}
ZADD key  0      Ottawa
ZADD key  201    Montreal
ZADD key  451    Toronto

ZRANGE key 0 -1               # show all items in set

ZRANGEBYSCORE key -inf 300    # all items with score up to 300
ZREMRANGEBYSCORE key 200 300  # remove all items with scores between 200 and 300

Hashes

https://redis.io/commands#hash

HKEYS   key                                # list all keys in hash

HGET    key mapkey-2
HGETALL key
HMGET   key mapkey-1 mapkey-2              # get hash-map value


HSET    key mapkey-1 val-1                 # create/update single hash-map value
HMSET   key mapkey-1 val-1 mapkey-2 val-2  # create/update multiple hash-map values

HyperLogLogs

Stores and counts unique entries in a set in a memory optimized way.

PFADD key a a b c   # add 4x items to a hyperloglog 

PFCOUNT key         # 3 (num of unique items)