Introduction to redis using Lua script

1. Basic usage

1.1 EVAL script numkeys key [key …] arg [arg …]

numkeys yes key The number of , Write later key1 key2… val1 val2…, give an example

127.0.0.1:6379> eval "return {KEYS[1],KEYS[2],ARGV[1],ARGV[2]}" 2 key1 key2 val1 val2
1) "key1"
2) "key2"
3) "val1"
4) "val2"

1.2 SCRIPT LOAD script

Load the script into the script cache , return SHA1 The checksum . But it will not be implemented immediately , give an example

127.0.0.1:6379> SCRIPT LOAD "return 'hello world'"
"5332031c6b470dc5a0dd9b4bf2030dea6d65de91"

1.3 EVALSHA sha1 numkeys key [key …] arg [arg …]

Execute the script content according to the cache code . give an example

127.0.0.1:6379> SCRIPT LOAD "return {KEYS[1],KEYS[2],ARGV[1],ARGV[2]}" 
"a42059b356c875f0717db19a51f6aaca9ae659ea"
127.0.0.1:6379> EVALSHA "a42059b356c875f0717db19a51f6aaca9ae659ea" 2 key1 key2 val1 val2
1) "key1"
2) "key2"
3) "val1"
4) "val2"

1.4 SCRIPT EXISTS script [script …]

adopt sha1 Check and determine whether the script is in the cache

1.5 SCRIPT FLUSH

Empty cache

127.0.0.1:6379> SCRIPT LOAD "return 'hello jihite'"
"3a43944275256411df941bdb76737e71412946fd"
127.0.0.1:6379> SCRIPT EXISTS "3a43944275256411df941bdb76737e71412946fd"
1) (integer) 1
127.0.0.1:6379> SCRIPT FLUSH
OK
127.0.0.1:6379> SCRIPT EXISTS "3a43944275256411df941bdb76737e71412946fd"
1) (integer) 0

1.6 SCRIPT KILL

Kill the currently executing script

2. The main advantage

Reduce network overhead ： Multiple requests are sent by script at one time , Reduce network latency

Atomic manipulation ： Execute the script as a whole , No other commands will be inserted in the middle , No need to use transactions

Reuse ： The script sent by the client is permanent redis in , Other clients can reuse scripts

Embeddable sex ： Embeddable JAVA,C# And many other programming languages , Support cross platform interaction of different operating systems

3. actual combat

Directly in redis-cli Direct writing lua Script , This is very inconvenient to edit , Usually we put lua script In a lua In file , Then execute this lua Script ,

** Example ： Active user judgment ：** Determine whether a game user is an active user , If it meets the standard , Then the number of active users +1

if redis.call("EXISTS",KEYS[1]) == 1 then
     return redis.call("INCRBY",KEYS[1],ARGV[1])
   else
     return nil
   end

Storage location ：

/Users/jihite/activeuser.lua

perform

$ redis-cli --eval /Users/jihite/activeuser.lua user , 1
(integer) 1

127.0.0.1:6379> get user
"1"
127.0.0.1:6379> exit
$ redis-cli --eval /Users/jihite/activeuser.lua user , 1
(integer) 2
$ redis-cli 
127.0.0.1:6379> get user
"2"
127.0.0.1:6379> exit
$ redis-cli --eval /Users/jihite/activeuser.lua user , 4
(integer) 6

4. Script security

Such as the command to generate random numbers , If in master After the execution of , And then slave The execution will be different , This destroys the consistency of the master and slave nodes

To solve this problem , Redis Yes Lua There is a strict limit on the scripts that the environment can execute —— All scripts must be pure functions without side effects （pure function）. All the situations just mentioned don't exist at all .Redis Yes Lua The environment has made a series of corresponding measures ：

• No library to access system state （ For example, system time library ）
• No use loadfile function
• If the script is executing commands with random properties （ such as RANDOMKEY ）, Or commands with side effects （ such as TIME ） after , Trying to execute a write command （ such as SET ）, that Redis Will prevent this script from continuing , And return an error .
• If the script executes a random read command （ such as SMEMBERS ）, Then the output of the script is returned to Redis Before , An automatic lexicographic sort will be performed first , So as to ensure that the output results are orderly .
• use Redis Self defined random generating function , Replace Lua Environment math Table original math.random Functions and math.randomseed function , The new function has such properties ： Every time you execute Lua Script time , Unless you explicitly call math.randomseed , otherwise math.random The generated pseudo-random number sequence is always the same .

Reference resources

https://www.runoob.com/redis/redis-scripting.html （ Basic use ）

https://www.cnblogs.com/Don/articles/5731856.html ( example )

https://www.cnblogs.com/huangxincheng/p/6230129.html

https://redisbook.readthedocs.io/en/latest/feature/scripting.html#lua （ Security ）

https://blog.csdn.net/demon7552003/article/details/120165160 Redis And Lua Detailed explanation