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Strings

  • Strings are the most basic kind of Redis value
  • Redis Strings are binary safe
  • A Redis string can contain any kind of data, for instance a JPEG image or a serialized Ruby object
> set a1 10
> get a1

SET Vs GET

  • SET and the GET commands are the way we set and retrieve a string value
  • SET performs an assignment
  • SET will replace any existing value already stored into the key
  • Values can be strings (including binary data) of every kind, for instance you can store a jpeg image inside a key

Set Command

  • The SET command has interesting options, that are provided as additional arguments

EX seconds 

Set the specified expire time, in seconds

PX milliseconds 

Set the specified expire time, in milliseconds

NX 

Only set the key if it does not already exist

XX 

Only set the key if it already exist

Example:

127.0.0.1:6379> get a1
"100"
127.0.0.1:6379> set a1 101 xx
OK
127.0.0.1:6379> get a1
"101"
127.0.0.1:6379> set a1 102 nx
(nil)
127.0.0.1:6379> get a1
"101"
127.0.0.1:6379>

Altering & Querying Redis Keyspace

  • EXISTS command returns 1 or 0 to signal if a given key exists or not in the database
  • DEL command deletes a key and associated value, whatever the value is
    • Returns 1 or 0 depending on whether the key was removed
  • These commands can be used on all keys regardless of the value 
data structure

Example:

127.0.0.1:6379> set z1 hello
OK
127.0.0.1:6379> exists z1
(integer) 1
127.0.0.1:6379> del z1
(integer) 1
127.0.0.1:6379> exists z1
(integer) 0
127.0.0.1:6379>

String with Integer Values - INCR

  • Use Strings as atomic counters using commands in the INCR family: 
    • INCR, 
    • DECR, 
    • INCRBY,
    • DECRBY
  • Even if strings are the basic values of Redis, there are interesting operations you can perform with them
  • For instance, one is atomic increment

Example:

127.0.0.1:6379> set counter 100
OK
127.0.0.1:6379> incr counter
(integer) 101
127.0.0.1:6379> incr counter
(integer) 102
127.0.0.1:6379> incrby counter 50
(integer) 152
127.0.0.1:6379>

MSET and MGET

  • MSET and MGET commands enable to set or retrieve the value of multiple keys in a single command is also useful for reduced latency

Example:

127.0.0.1:6379> mset a 10 b 20 c 30
OK
127.0.0.1:6379> mget a b c 
1) "10"
2) "20"
3) "30"
127.0.0.1:6379>
  • GETSET command sets a key to a new value, returning the old value as the result

Keys Expiration

  • Set using seconds or milliseconds precision
  • However the expire time resolution is always 1 millisecond
  • Information about expires are 
replicated and persisted on disk, 
the time virtually passes when your 
Redis server remains stopped
  • Redis saves the date when
a key will expire

Example:

127.0.0.1:6379> set key 150
OK
127.0.0.1:6379> expire key 10
(integer) 1
127.0.0.1:6379> ttl key
(integer) 5
127.0.0.1:6379> get key
(nil)
127.0.0.1:6379>