Redis persistence

Single point Redis There are many problems , Therefore, persistence is required Redis：

One 、RDB Persistence

RDB Full name Redis Database Backup file（Redis Data backup file ）, It's also called Redis Data snapshot . Simply put, it is to record all the data in memory to disk . When Redis After instance failure and restart , Read snapshot file from disk , Restore data . The snapshot file is called RDB file , By default, it is saved in the current running Directory .

Execution opportunity 、

1、save command :

 2、bgsave command ：

 3、 During shutdown ：

Redis During shutdown, it will be executed once save command , Realization RDB Persistence .

4、 Trigger RDB Conditions ：

Redis There is an internal trigger RDB The mechanism of , Can be in redis.conf Found in file , The format is as follows ：

RDB Other configurations of can also be in redis.conf Set in file ：

principle 、

bgsave At the beginning fork The main process gets the child process , Child processes share the memory data of the main process . complete fork After reading the memory data and writing RDB file .fork It's using copy-on-write technology ：

summary 、

Two 、AOF Persistence

AOF Its full name is Append Only File（ Additional documents ）.Redis Every write command processed will be recorded in AOF file , It can be regarded as a command log file .

  The configuration file 、

AOF The default is off , Need modification redis.conf Configuration file to open AOF：

AOF The frequency of command recording can also be through redis.conf File to match ：

Comparison of three recording frequency modes ：

File rewriting 、

Because it's a record command ,AOF The document will compare with RDB The files are much bigger . and AOF Will record for the same key Multiple write operations , But only the last write operation makes sense . Through execution bgrewriteaof command , It can make AOF The file performs the rewriting function , Achieve the same effect with the least number of commands .

Redis It will also be automatically rewritten when the threshold is triggered AOF file . The threshold can also be in redis.conf Middle configuration ：

 

3、 ... and 、RDB And AOF contrast