Redis expired key cleaning and deletion policy summary

Redis The bottom layer uses three strategies to clean up expired key

One 、 Passive cleaning

The trigger condition ： read / Write an expired key

When reading and writing a key when ,Redis First check key Whether there is , If it exists and has expired , Delete key Back at the same time nil To the client

Two 、 Regular clearance

The trigger condition ：Redis Regular inspection

redis Cleaning up expired items will be performed regularly key The task of , The operating frequency is determined by redis.conf Medium hz Parameter determination , Value range 1~500, The default is 10, Run per second 10 Time .

The cleaning process is as follows ：

1） Traverse all db
2） from db With the expiration time set in key Random check in the set of 20 individual key
3） Delete all expired items found in the check key
4） If the inspection result is 25% The above key Has expired , Then continue to repeat step 2-3, Otherwise, continue to traverse the next db

turn up hz Will improve redis The frequency with which periodic tasks are performed , If redis Contains many expired key Words , Consider increasing this value , But note that it will also increase CPU The pressure of the ,redis The author suggests that this value should not exceed 100.

3、 ... and 、 Mandatory deletion

The trigger condition ：Redis Use memory to maxmemory Configuration of , And then according to maxmemory-policy To clean up expired key

Concrete maxmemory-policy Please refer to my previous articles ：Redis LRU Cache recovery mechanism _ Pan Guangyu de Xiaobai's blog -CSDN Blog

The cleaning process is blocked , It won't stop until enough memory space is cleared

Reference resources ：

redis Be overdue key Delete policy for _ free de Bike blog -CSDN Blog _redis Of key Will it be deleted automatically