Redis is in the family of databases called key-value stores.
The essence of a key-value store is the ability to store some data, called a value, inside a key. This data can later be retrieved only if we know the exact key used to store it.
Often Redis it is called a data structure server because it has outer key-value shell, but each value can contain a complex data structure, such as a string, a list, a hashes, or ordered data structures called sorted sets as well as probabilistic data structures like hyperloglog.
Server Startup
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| redis-server # start the server
redis-cli
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| Bash |
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| SET <key> <value> [ EX <seconds> ] # store a key-value pair, TTL optional
GET <key> # read a key content
EXISTS <key> # check if a key exists
DEL <key> # delete a key-value pair
INCR <key> # atomically increment a number stored at a given key
INCRBY <key> <amount> # increment the number contained inside a key by a specific amount
DECR <key>
DECRBY <key> <amount>
# re-setting the key will make it permanent (TTL -1)
EXPIRE <key> <seconds> # make the key expire after <second> seconds
TTL <key> # see remaining seconds before expiry
PEXPIRE <key> <seconds> # make the key expire after <second> milli-seconds
PTTL <key> # see remaining milli-seconds before expiry
PERSIST <key> # make the key permanent
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A list is a series of ordered values.
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| RPUSH <key> <value1> <value2> ... # add one or more values to the end of the list
LPUSH <key> <value1> <value2> ... # add one or more values to the start of a list
LLEN # number of items in the list
LRANGE <key> <start_index> <end_index> # return a subset of the list, end index included. Negative indexes count backwards from the end
LPOP # remove and return the first item fro the list
RPOP # remove and return the last item fro the list
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A set is similar to a list, except it does not have a specific order and each element may only appear once.
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| SADD <key> <value1> <value2> ... # add one or more values to the set (return 0 if values are already inside)
SREM <key> <value> # remove the given member from the set, return 1 or 0 to signal if the member was actually there or not.
SPOP <key> <value> # remove and return value from the set
SISMEMBER <key> <value> # test if value is in the set
SMEMBERS <key> # lis of all set items
SUINION <key1> <key2> ... # combine two or more sets and return the list of all elements.
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Sets are a very handy data type, but as they are unsorted they don't work well for a number of problems. This is why Redis 1.2 introduced Sorted Sets.
A sorted set is similar to a regular set, but now each value has an associated score. This score is used to sort the elements in the set.
| Bash |
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| ZADD <key> <score> <value> # add a value with it's score
ZRANGE <key> <start_index> <end_index> # return a subset of the sortedSet
...
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Hashes are maps between string fields and string values, so they are the perfect data type to represent objects.
| Bash |
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| HSET <key> <field> <value> [ <field> <value> ... ] # set the string of a hash field
HSETNX <key> <field> <value> # set the value of a hash field, only if the field does not exist
HEXISTS <key> <field> # determine if a hash field exists
HLEN <key> # get the number of fields in a hash
HSTRLEN <key> <field> # get the length of the value of a hash field
HGETALL <key> # get all fields and values in a hash
HGET <key> <field> # get data on a single field
HKEYS <key> # get all the fields in a hash
HVALS <key> # get all the values in a hash
HDEL <key> <field_1> <field_2> ... # delete one or more field hashes
HMGET <key> <field> [<field> ...] # get the values of all the given hash fields
HMSET <key> <field> <value> [<field> <value> ...] # set multiple hash fields to multiple values
HINCRBY <key> <field> <amount> # increment the integer value of a hash field by the given number
HINCRBYFLOAT <key> <field> <amount> # increment the float value of a hash field by the given amount
HSCAN <key> <cursor> [MATCH <pattern>] [COUNT <count>] # incrementally iterate hash fields and associated values
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