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redis过期策略复习

Nicksxs

之前其实写过redis的过期的一些原理,这次主要是记录下,一些使用上的概念,主要是redis使用的过期策略是懒过期和定时清除,懒过期的其实比较简单,即是在key被访问的时候会顺带着判断下这个key是否已过期了,如果已经过期了,就不返回了,但是这种策略有个漏洞是如果有些key之后一直不会被访问了,就等于沉在池底了,所以需要有一个定时的清理机制,去从设置了过期的key池子(expires)里随机地捞key,具体的策略我们看下官网的解释

  1. Test 20 random keys from the set of keys with an associated expire.
  2. Delete all the keys found expired.
  3. If more than 25% of keys were expired, start again from step 1.

从池子里随机获取20个key,将其中过期的key删掉,如果这其中有超过25%的key已经过期了,那就再来一次,以此保持过期的key不超过25%(左右),并且这个定时策略可以在redis的配置文件

# Redis calls an internal function to perform many background tasks, like
# closing connections of clients in timeout, purging expired keys that are
# never requested, and so forth.
#
# Not all tasks are performed with the same frequency, but Redis checks for
# tasks to perform according to the specified "hz" value.
#
# By default "hz" is set to 10. Raising the value will use more CPU when
# Redis is idle, but at the same time will make Redis more responsive when
# there are many keys expiring at the same time, and timeouts may be
# handled with more precision.
#
# The range is between 1 and 500, however a value over 100 is usually not
# a good idea. Most users should use the default of 10 and raise this up to
# 100 only in environments where very low latency is required.
hz 10

可以配置这个hz的值,代表的含义是每秒的执行次数,默认是10,其实也用了hz的普遍含义。有兴趣可以看看之前写的一篇文章redis系列介绍七-过期策略

本文使用「署名 4.0 国际 (CC BY 4.0)」许可协议,欢迎转载、或重新修改使用,但需要注明来源。 署名 4.0 国际 (CC BY 4.0)
本文作者: Nicksxs
创建时间: 2021-07-25
本文链接: redis过期策略复习

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