Redis learning notes - data type: string (string)

The string is Redis The most basic data structure . First, the key is a string type , And several other types are built on the basis of string types . A value of type string can actually be a string （ Simple string 、 Complex string （ for example JSON、XML））、 Numbers （ Integers 、 Floating point numbers ）, Even binary （ picture 、 Audio 、 video ）, But the maximum value cannot exceed 512MB.

Set the value

set command

set key value [ex seconds] [px milliseconds] [nx|xx]

ex seconds： Sets a second - level expiration time for the key

127.0.0.1:6379> set hello world ex 50
OK

px milliseconds： Sets the millisecond expiration time for the key .

127.0.0.1:6379> set hello world px 50000
OK

nx： The key must not exist , Can be set successfully , Used to add .

127.0.0.1:6379> set hello world nx
OK
127.0.0.1:6379> set hello world nx
(nil)

xx： And nx contrary , The bond has to exist , Can be set successfully , Used to update the .

127.0.0.1:6379> del hello
(integer) 1
127.0.0.1:6379> set hello world xx
(nil)
127.0.0.1:6379> set hello world
OK
127.0.0.1:6379> set hello world1 xx
OK

setex command （ Set expiration time ）

setex key seconds value

The following four examples are all settings key by hello Cache expiration time 50 second

127.0.0.1:6379> setex hello 50 world
OK
127.0.0.1:6379> set hello world ex 50
OK
127.0.0.1:6379> set hello world px 50000
OK
127.0.0.1:6379> expire java 50
(integer) 1

setnx command （ If key There is no operation , If not, create ）

setnx key value

because Redis The single thread command processing mechanism , If multiple clients execute at the same time setnx key value, according to setnx Only one client can be set successfully ,setnx It can be used as an implementation of distributed lock ,Redis The use of setnx How to implement distributed lock ：http://redis.io/topics/distlock.

Get value

get key

Batch setting value

mset key value [key value ...]

Batch settings a,b,c Three key

127.0.0.1:6379> mset a 1 b 2 c 3
OK

Get values in batch and return them in sequence

mget key [key ...]

Batch acquisition a,b,c Three key value

127.0.0.1:6379> mget a b c
1) "1"
2) "2"
3) "3"

Batch operations can reduce items and redis Network request for database , If you loop through each , Then each one should go through the network request , Compared with memory speed , The network is absolutely the bottleneck of performance , So the batch operation is entrusted to redis Internal processing , One request , One return , It helps to improve the efficiency of business processing ; But it should be noted that the number of commands sent by each batch operation is not unlimited , If the quantity is too large, it may cause Redis Congestion or network congestion .

Count

Self increasing

incr key

Self reduction

decr key

Self increment specified number

incr key increment

Self subtract the specified number

decrby key decrement

Self-incremented floating point number

incrbyfloat key increment

Many storage systems and programming languages are used internally CAS Mechanism to achieve the counting function , There will be a certain amount of CPU expenses , But in Redis There is no such problem in , because Redis It's a single thread architecture , Any order arrived Redis The server should execute in sequence .

Additional value

append key value

Illustrate with examples ：

127.0.0.1:6379> get hello
"world"
127.0.0.1:6379> append hello is
(integer) 7
127.0.0.1:6379> get hello
"worldis"

Get string length

strlen key

Illustrate with examples ：

127.0.0.1:6379> set hello world
OK
127.0.0.1:6379> strlen hello
(integer) 5

Set and return the value （ If there is an original value, the original value will be returned ）

getset key value

Illustrate with examples ：

127.0.0.1:6379> get hello
"world"
127.0.0.1:6379> getset hello world1
"world"
127.0.0.1:6379> get hello
"world1"

Sets the character of the specified position

setrange key offeset value

Illustrate with examples ：

127.0.0.1:6379> set java redis
OK
127.0.0.1:6379> setrange java 0 j
(integer) 5
127.0.0.1:6379> get java
"jedis"

Get part string

getrange key start end

Illustrate with examples ：

127.0.0.1:6379> get java
"jedis"
127.0.0.1:6379> getrange java 1 3
"edi"

Check the internal code

127.0.0.1:6379> object encoding hello
"embstr"

The internal encoding of a string type is 3 Kind of ：

• int：8 A long integer of bytes .
• embstr： Less than or equal to 39 A byte string .
• raw： Greater than 39 A byte string .

Redis Depending on the type and length of the current value, which internal encoding is used to implement .

Typical usage scenarios （ Three examples ）

1. Do things that storage tiers don't change very often , But a cache layer of data that is often accessed , Reduce database pressure

2. Be a user session The memory of , Solve the problem of distributed service load balancing session Out of sync problem

3. Count , For example, the number of page views , Video playback volume , If you call the interface to save the database every time, it will cause a large number of requests , Greatly affects performance , Can exist first redis, And then persistence