redis内存淘汰策略-------Reservoir Sampling(水库采样)

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已于 2025-04-18 17:13:31 修改

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分类专栏： Redis 文章标签： redis 数据库缓存随机采样水库采样 Reservoir evict

于 2024-08-11 17:40:33 首次发布

本文链接：https://blog.youkuaiyun.com/weixin_46290302/article/details/141088762

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文章目录

过期删除策略和内存淘汰策略
- 内存淘汰策略
- - evictionPoolEntry
  - evictionPoolPopulate
Reservoir Sampling

过期删除策略和内存淘汰策略

详细介绍请参考博客“redis过期删除策略和内存淘汰策略”

内存淘汰策略

为了节省内存，redis并没有采用传统的方法实现LRU和LFU而是基于随机采样的方式，近似实现LRU和LFU，并引入淘汰池进行优化。接下来详细看看是如何淘汰池进行优化的。具体实现在"evict.c"文件中的函数"evictionPoolPopulate"。

/* This is a helper function for performEvictions(), it is used in order
 * to populate the evictionPool with a few entries every time we want to
 * expire a key. Keys with idle time bigger than one of the current
 * keys are added. Keys are always added if there are free entries.
 *
 * We insert keys on place in ascending order, so keys with the smaller
 * idle time are on the left, and keys with the higher idle time on the
 * right. */
 这个函数是"performEvictions()"的辅助函数。每当想要过期一些key时该函数被用来向淘汰池填充一些数据。
 当淘汰池未满时，keys总是被添加；反之的话，添加具有更大idle time的keys。
 淘汰池按照idle time升序排序，即较小idle time的key存储在淘汰池的左边，较大idle time的key存储在淘汰池的右边。

 /* When an LFU policy is used instead, a reverse frequency indication is used
 * instead of the idle time, so that we still evict by larger value (larger
 * inverse frequency means to evict keys with the least frequent accesses).*/
 当使用LFU策略时，用反向频率reverse frequency代替idle time。
 按照reverse frequency升序排序，较大的inverse frequency意味着keys具有较小的lfu值即least frequent accesses。