You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
805 lines
116 KiB
805 lines
116 KiB
<!DOCTYPE html>
|
|
<html lang="zh-Hans">
|
|
<head>
|
|
<meta charset="UTF-8">
|
|
<meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=2">
|
|
<meta name="theme-color" content="#222">
|
|
<meta name="generator" content="Hexo 4.2.0">
|
|
<link rel="apple-touch-icon" sizes="180x180" href="/images/apple-touch-icon-next.png">
|
|
<link rel="icon" type="image/png" sizes="32x32" href="/images/favicon-32x32-next.png">
|
|
<link rel="icon" type="image/png" sizes="16x16" href="/images/favicon-16x16-next.png">
|
|
<link rel="mask-icon" href="/images/logo.svg" color="#222">
|
|
<meta name="google-site-verification" content="2X6S9P7CAjXjVvw8YyQR8pCu-B0oEu7O9quLgxXuWyA">
|
|
<meta name="baidu-site-verification" content="dV8JGNzi0c">
|
|
<meta name="chinaz-site-verification" content="500A176AA29CFB31">
|
|
|
|
<script data-ad-client="ca-pub-7480618470784058" async src="https://pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script>
|
|
|
|
<link rel="stylesheet" href="/css/main.css">
|
|
|
|
<link rel="stylesheet" href="//fonts.loli.net/css?family=Lato:300,300italic,400,400italic,700,700italic|M+ 2p:300,300italic,400,400italic,700,700italic&display=swap&subset=latin,latin-ext">
|
|
<link rel="stylesheet" href="/lib/font-awesome/css/all.min.css">
|
|
<link rel="stylesheet" href="//cdn.jsdelivr.net/gh/fancyapps/fancybox@3/dist/jquery.fancybox.min.css">
|
|
|
|
<script id="hexo-configurations">
|
|
var NexT = window.NexT || {};
|
|
var CONFIG = {"hostname":"nicksxs.me","root":"/","scheme":"Pisces","version":"7.8.0","exturl":false,"sidebar":{"position":"left","display":"post","padding":18,"offset":12,"onmobile":false},"copycode":{"enable":true,"show_result":false,"style":null},"back2top":{"enable":true,"sidebar":false,"scrollpercent":false},"bookmark":{"enable":false,"color":"#222","save":"auto"},"fancybox":true,"mediumzoom":false,"lazyload":true,"pangu":false,"comments":{"style":"tabs","active":null,"storage":true,"lazyload":false,"nav":null},"algolia":{"hits":{"per_page":10},"labels":{"input_placeholder":"Search for Posts","hits_empty":"We didn't find any results for the search: ${query}","hits_stats":"${hits} results found in ${time} ms"}},"localsearch":{"enable":false,"trigger":"auto","top_n_per_article":1,"unescape":false,"preload":false},"motion":{"enable":true,"async":false,"transition":{"post_block":"fadeIn","post_header":"slideDownIn","post_body":"slideDownIn","coll_header":"slideLeftIn","sidebar":"slideUpIn"}}};
|
|
</script>
|
|
|
|
<meta name="description" content="LRU说完了过期策略再说下淘汰策略，redis 使用的策略是近似的 lru 策略，为什么是近似的呢，先来看下什么是 lru，看下 wiki 的介绍，图中一共有四个槽的存储空间，依次访问顺序是 A B C D E D F，当第一次访问 D 时刚好占满了坑，并且值是 4，这个值越小代表越先被淘汰，当 E 进来时，看了下已经存在的四个里 A 是最小的，代表是最早存在并且最早被访问的，那就先淘汰它了，E">
|
|
<meta property="og:type" content="article">
|
|
<meta property="og:title" content="redis系列介绍八-淘汰策略">
|
|
<meta property="og:url" content="https://nicksxs.me/2020/04/18/redis%E7%B3%BB%E5%88%97%E4%BB%8B%E7%BB%8D%E5%85%AB/index.html">
|
|
<meta property="og:site_name" content="Nicksxs's Blog">
|
|
<meta property="og:description" content="LRU说完了过期策略再说下淘汰策略，redis 使用的策略是近似的 lru 策略，为什么是近似的呢，先来看下什么是 lru，看下 wiki 的介绍，图中一共有四个槽的存储空间，依次访问顺序是 A B C D E D F，当第一次访问 D 时刚好占满了坑，并且值是 4，这个值越小代表越先被淘汰，当 E 进来时，看了下已经存在的四个里 A 是最小的，代表是最早存在并且最早被访问的，那就先淘汰它了，E">
|
|
<meta property="og:image" content="https://i.loli.net/2020/04/14/wWyhc2dQfb4BYsK.png">
|
|
<meta property="og:image" content="https://i.loli.net/2020/04/18/QwcROpB345ezEkX.png">
|
|
<meta property="article:published_time" content="2020-04-18T15:23:41.000Z">
|
|
<meta property="article:modified_time" content="2020-04-19T09:28:42.555Z">
|
|
<meta property="article:author" content="Nicksxs">
|
|
<meta property="article:tag" content="Redis">
|
|
<meta property="article:tag" content="C语言">
|
|
<meta property="article:tag" content="数据结构">
|
|
<meta property="article:tag" content="源码">
|
|
<meta property="article:tag" content="源码分析">
|
|
<meta property="article:tag" content="过期策略">
|
|
<meta property="article:tag" content="淘汰策略">
|
|
<meta property="article:tag" content="expire">
|
|
<meta property="article:tag" content="LFU">
|
|
<meta name="twitter:card" content="summary">
|
|
<meta name="twitter:image" content="https://i.loli.net/2020/04/14/wWyhc2dQfb4BYsK.png">
|
|
|
|
<link rel="canonical" href="https://nicksxs.me/2020/04/18/redis%E7%B3%BB%E5%88%97%E4%BB%8B%E7%BB%8D%E5%85%AB/">
|
|
|
|
|
|
<script id="page-configurations">
|
|
// https://hexo.io/docs/variables.html
|
|
CONFIG.page = {
|
|
sidebar: "",
|
|
isHome : false,
|
|
isPost : true,
|
|
lang : 'zh-Hans'
|
|
};
|
|
</script>
|
|
|
|
<title>redis系列介绍八-淘汰策略 | Nicksxs's Blog</title>
|
|
|
|
<script async src="https://www.googletagmanager.com/gtag/js?id=UA-61358619-1"></script>
|
|
<script>
|
|
if (CONFIG.hostname === location.hostname) {
|
|
window.dataLayer = window.dataLayer || [];
|
|
function gtag(){dataLayer.push(arguments);}
|
|
gtag('js', new Date());
|
|
gtag('config', 'UA-61358619-1');
|
|
}
|
|
</script>
|
|
|
|
|
|
<script>
|
|
var _hmt = _hmt || [];
|
|
(function() {
|
|
var hm = document.createElement("script");
|
|
hm.src = "https://hm.baidu.com/hm.js?20f33b3c0c0eff9b1522999c0015646d";
|
|
var s = document.getElementsByTagName("script")[0];
|
|
s.parentNode.insertBefore(hm, s);
|
|
})();
|
|
</script>
|
|
|
|
|
|
|
|
|
|
<noscript>
|
|
<style>
|
|
.use-motion .brand,
|
|
.use-motion .menu-item,
|
|
.sidebar-inner,
|
|
.use-motion .post-block,
|
|
.use-motion .pagination,
|
|
.use-motion .comments,
|
|
.use-motion .post-header,
|
|
.use-motion .post-body,
|
|
.use-motion .collection-header { opacity: initial; }
|
|
|
|
.use-motion .site-title,
|
|
.use-motion .site-subtitle {
|
|
opacity: initial;
|
|
top: initial;
|
|
}
|
|
|
|
.use-motion .logo-line-before i { left: initial; }
|
|
.use-motion .logo-line-after i { right: initial; }
|
|
</style>
|
|
</noscript>
|
|
|
|
<link rel="alternate" href="/atom.xml" title="Nicksxs's Blog" type="application/atom+xml">
|
|
</head>
|
|
|
|
<body itemscope itemtype="http://schema.org/WebPage">
|
|
<div class="container use-motion">
|
|
<div class="headband"></div>
|
|
|
|
<header class="header" itemscope itemtype="http://schema.org/WPHeader">
|
|
<div class="header-inner"><div class="site-brand-container">
|
|
<div class="site-nav-toggle">
|
|
<div class="toggle" aria-label="Toggle navigation bar">
|
|
<span class="toggle-line toggle-line-first"></span>
|
|
<span class="toggle-line toggle-line-middle"></span>
|
|
<span class="toggle-line toggle-line-last"></span>
|
|
</div>
|
|
</div>
|
|
|
|
<div class="site-meta">
|
|
|
|
<a href="/" class="brand" rel="start">
|
|
<span class="logo-line-before"><i></i></span>
|
|
<h1 class="site-title">Nicksxs's Blog</h1>
|
|
<span class="logo-line-after"><i></i></span>
|
|
</a>
|
|
<p class="site-subtitle" itemprop="description">What hurts more, the pain of hard work or the pain of regret?</p>
|
|
</div>
|
|
|
|
<div class="site-nav-right">
|
|
<div class="toggle popup-trigger">
|
|
</div>
|
|
</div>
|
|
</div>
|
|
|
|
|
|
|
|
|
|
<nav class="site-nav">
|
|
<ul id="menu" class="main-menu menu">
|
|
<li class="menu-item menu-item-home">
|
|
|
|
<a href="/" rel="section"><i class="home fa-fw"></i>Home</a>
|
|
|
|
</li>
|
|
<li class="menu-item menu-item-about">
|
|
|
|
<a href="/about/" rel="section"><i class="about fa-fw"></i>About</a>
|
|
|
|
</li>
|
|
<li class="menu-item menu-item-tags">
|
|
|
|
<a href="/tags/" rel="section"><i class="tags fa-fw"></i>Tags</a>
|
|
|
|
</li>
|
|
<li class="menu-item menu-item-categories">
|
|
|
|
<a href="/categories/" rel="section"><i class="categories fa-fw"></i>Categories</a>
|
|
|
|
</li>
|
|
<li class="menu-item menu-item-archives">
|
|
|
|
<a href="/archives/" rel="section"><i class="archives fa-fw"></i>Archives</a>
|
|
|
|
</li>
|
|
<li class="menu-item menu-item-sitemap">
|
|
|
|
<a href="/sitemap.xml" rel="section"><i class="sitemap fa-fw"></i>Sitemap</a>
|
|
|
|
</li>
|
|
<li class="menu-item menu-item-commonweal">
|
|
|
|
<a href="/404/" rel="section"><i class="heartbeat fa-fw"></i>Commonweal 404</a>
|
|
|
|
</li>
|
|
</ul>
|
|
</nav>
|
|
|
|
|
|
|
|
|
|
</div>
|
|
</header>
|
|
|
|
|
|
<div class="back-to-top">
|
|
<i class="fa fa-arrow-up"></i>
|
|
<span>0%</span>
|
|
</div>
|
|
|
|
<a href="https://github.com/nicksxs" class="github-corner" title="Follow me on GitHub" aria-label="Follow me on GitHub" rel="noopener" target="_blank"><svg width="80" height="80" viewBox="0 0 250 250" aria-hidden="true"><path d="M0,0 L115,115 L130,115 L142,142 L250,250 L250,0 Z"></path><path d="M128.3,109.0 C113.8,99.7 119.0,89.6 119.0,89.6 C122.0,82.7 120.5,78.6 120.5,78.6 C119.2,72.0 123.4,76.3 123.4,76.3 C127.3,80.9 125.5,87.3 125.5,87.3 C122.9,97.6 130.6,101.9 134.4,103.2" fill="currentColor" style="transform-origin: 130px 106px;" class="octo-arm"></path><path d="M115.0,115.0 C114.9,115.1 118.7,116.5 119.8,115.4 L133.7,101.6 C136.9,99.2 139.9,98.4 142.2,98.6 C133.8,88.0 127.5,74.4 143.8,58.0 C148.5,53.4 154.0,51.2 159.7,51.0 C160.3,49.4 163.2,43.6 171.4,40.1 C171.4,40.1 176.1,42.5 178.8,56.2 C183.1,58.6 187.2,61.8 190.9,65.4 C194.5,69.0 197.7,73.2 200.1,77.6 C213.8,80.2 216.3,84.9 216.3,84.9 C212.7,93.1 206.9,96.0 205.4,96.6 C205.1,102.4 203.0,107.8 198.3,112.5 C181.9,128.9 168.3,122.5 157.7,114.1 C157.9,116.9 156.7,120.9 152.7,124.9 L141.0,136.5 C139.8,137.7 141.6,141.9 141.8,141.8 Z" fill="currentColor" class="octo-body"></path></svg></a>
|
|
|
|
|
|
<main class="main">
|
|
<div class="main-inner">
|
|
<div class="content-wrap">
|
|
|
|
|
|
<div class="content post posts-expand">
|
|
|
|
|
|
|
|
|
|
|
|
<article itemscope itemtype="http://schema.org/Article" class="post-block" lang="zh-Hans">
|
|
<link itemprop="mainEntityOfPage" href="https://nicksxs.me/2020/04/18/redis%E7%B3%BB%E5%88%97%E4%BB%8B%E7%BB%8D%E5%85%AB/">
|
|
|
|
<span hidden itemprop="author" itemscope itemtype="http://schema.org/Person">
|
|
<meta itemprop="image" content="/uploads/avatar.jpg">
|
|
<meta itemprop="name" content="Nicksxs">
|
|
<meta itemprop="description" content="learn from zero,技术博客，Nicksxs，史学森">
|
|
</span>
|
|
|
|
<span hidden itemprop="publisher" itemscope itemtype="http://schema.org/Organization">
|
|
<meta itemprop="name" content="Nicksxs's Blog">
|
|
</span>
|
|
<header class="post-header">
|
|
<h1 class="post-title" itemprop="name headline">
|
|
redis系列介绍八-淘汰策略
|
|
</h1>
|
|
|
|
<div class="post-meta">
|
|
<span class="post-meta-item">
|
|
<span class="post-meta-item-icon">
|
|
<i class="far fa-calendar"></i>
|
|
</span>
|
|
<span class="post-meta-item-text">Posted on</span>
|
|
|
|
<time title="Created: 2020-04-18 23:23:41" itemprop="dateCreated datePublished" datetime="2020-04-18T23:23:41+08:00">2020-04-18</time>
|
|
</span>
|
|
<span class="post-meta-item">
|
|
<span class="post-meta-item-icon">
|
|
<i class="far fa-calendar-check"></i>
|
|
</span>
|
|
<span class="post-meta-item-text">Edited on</span>
|
|
<time title="Modified: 2020-04-19 17:28:42" itemprop="dateModified" datetime="2020-04-19T17:28:42+08:00">2020-04-19</time>
|
|
</span>
|
|
<span class="post-meta-item">
|
|
<span class="post-meta-item-icon">
|
|
<i class="far fa-folder"></i>
|
|
</span>
|
|
<span class="post-meta-item-text">In</span>
|
|
<span itemprop="about" itemscope itemtype="http://schema.org/Thing">
|
|
<a href="/categories/Redis/" itemprop="url" rel="index"><span itemprop="name">Redis</span></a>
|
|
</span>
|
|
,
|
|
<span itemprop="about" itemscope itemtype="http://schema.org/Thing">
|
|
<a href="/categories/Redis/%E6%95%B0%E6%8D%AE%E7%BB%93%E6%9E%84/" itemprop="url" rel="index"><span itemprop="name">数据结构</span></a>
|
|
</span>
|
|
,
|
|
<span itemprop="about" itemscope itemtype="http://schema.org/Thing">
|
|
<a href="/categories/C/" itemprop="url" rel="index"><span itemprop="name">C</span></a>
|
|
</span>
|
|
,
|
|
<span itemprop="about" itemscope itemtype="http://schema.org/Thing">
|
|
<a href="/categories/Redis/%E6%BA%90%E7%A0%81/" itemprop="url" rel="index"><span itemprop="name">源码</span></a>
|
|
</span>
|
|
,
|
|
<span itemprop="about" itemscope itemtype="http://schema.org/Thing">
|
|
<a href="/categories/C/Redis/" itemprop="url" rel="index"><span itemprop="name">Redis</span></a>
|
|
</span>
|
|
</span>
|
|
|
|
|
|
<span id="/2020/04/18/redis%E7%B3%BB%E5%88%97%E4%BB%8B%E7%BB%8D%E5%85%AB/" class="post-meta-item leancloud_visitors" data-flag-title="redis系列介绍八-淘汰策略" title="Views">
|
|
<span class="post-meta-item-icon">
|
|
<i class="fa fa-eye"></i>
|
|
</span>
|
|
<span class="post-meta-item-text">Views: </span>
|
|
<span class="leancloud-visitors-count"></span>
|
|
</span>
|
|
<span class="post-meta-item" title="Views" id="busuanzi_container_page_pv" style="display: none;">
|
|
<span class="post-meta-item-icon">
|
|
<i class="fa fa-eye"></i>
|
|
</span>
|
|
<span class="post-meta-item-text">Views: </span>
|
|
<span id="busuanzi_value_page_pv"></span>
|
|
</span>
|
|
|
|
<span class="post-meta-item">
|
|
|
|
<span class="post-meta-item-icon">
|
|
<i class="far fa-comment"></i>
|
|
</span>
|
|
<span class="post-meta-item-text">Disqus: </span>
|
|
|
|
<a title="disqus" href="/2020/04/18/redis%E7%B3%BB%E5%88%97%E4%BB%8B%E7%BB%8D%E5%85%AB/#disqus_thread" itemprop="discussionUrl">
|
|
<span class="post-comments-count disqus-comment-count" data-disqus-identifier="2020/04/18/redis系列介绍八/" itemprop="commentCount"></span>
|
|
</a>
|
|
</span>
|
|
|
|
|
|
|
|
</div>
|
|
</header>
|
|
|
|
|
|
|
|
|
|
<div class="post-body" itemprop="articleBody">
|
|
|
|
|
|
<h3 id="LRU"><a href="#LRU" class="headerlink" title="LRU"></a>LRU</h3><p>说完了过期策略再说下淘汰策略，redis 使用的策略是近似的 lru 策略，为什么是近似的呢，先来看下什么是 lru，看下 wiki 的介绍<br><img data-src="https://i.loli.net/2020/04/14/wWyhc2dQfb4BYsK.png" alt="">，图中一共有四个槽的存储空间，依次访问顺序是 A B C D E D F，<br>当第一次访问 D 时刚好占满了坑，并且值是 4，这个值越小代表越先被淘汰，当 E 进来时，看了下已经存在的四个里 A 是最小的，代表是最早存在并且最早被访问的，那就先淘汰它了，E 占领了 A 的位置，并设置值为 4，然后又访问 D 了，D 已经存在了，不过又被访问到了，得更新值为 5，然后是 F 进来了，这时 B 是最老的且最近未被访问，所以就淘汰它了。以上是一个 lru 的简要说明，但是 redis 没有严格按照这个去执行，理由跟前面过期策略一致，最严格的过期策略应该是每个 key 都有对应的定时器，当超时时马上就能清除，但是问题是这样的cpu 消耗太大，所换来的内存效率不太值得，淘汰策略也是这样，类似于上图，要维护所有 key 的一个有序 lru 值，并且遍历将最小的淘汰，redis 采用的是抽样的形式，最初的实现方式是随机从 dict 抽取 5 个 key，淘汰一个 lru 最小的，这样子勉强能达到淘汰的目的，但是效果不是特别好，后面在 redis 3.0开始，将随机抽取改成了维护一个 pool，pool 的大小默认是 16，每次放入的都是按lru 值有序排列好，每一次放入的必须是 lru小于 pool 中最小的 lru 才允许放入，直到放满，后面再有新的就会将大的踢出。<br>redis 针对这个策略的改进做了一个实验，这里借用下图<br><img data-src="https://i.loli.net/2020/04/18/QwcROpB345ezEkX.png" alt=""><br>首先背景是这图中的所有点都对应一个 redis 的 key，灰色部分加入后被顺序访问过一遍，然后又加入了绿色部分，那么按照理论的 lru 算法，应该是图左上中，浅灰色部分全都被淘汰，那么对比来看看图右上，左下和右下，左下表示 2.8 版本就是随机抽样 5 个 key，淘汰其中 lru 最小的一个，发现是灰色和浅灰色的都有被淘汰的，右下的 3.0 版本抽样数量不变的情况下，稍好一些，当 3.0 版本的抽样数量调整成 10 后，已经较为接近理论上的 lru 策略了，通过代码来简要分析下</p>
|
|
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">typedef</span> <span class="class"><span class="keyword">struct</span> <span class="title">redisObject</span> {</span></span><br><span class="line"> <span class="keyword">unsigned</span> type:<span class="number">4</span>;</span><br><span class="line"> <span class="keyword">unsigned</span> encoding:<span class="number">4</span>;</span><br><span class="line"> <span class="keyword">unsigned</span> lru:LRU_BITS; <span class="comment">/* LRU time (relative to global lru_clock) or</span></span><br><span class="line"><span class="comment"> * LFU data (least significant 8 bits frequency</span></span><br><span class="line"><span class="comment"> * and most significant 16 bits access time). */</span></span><br><span class="line"> <span class="keyword">int</span> refcount;</span><br><span class="line"> <span class="keyword">void</span> *ptr;</span><br><span class="line">} robj;</span><br></pre></td></tr></table></figure>
|
|
<p>对于 lru 策略来说，lru 字段记录的就是<a href="https://github.com/antirez/redis/blob/unstable/src/server.h#L603" target="_blank" rel="noopener"><code>redisObj</code></a> 的LRU time，<br>redis 在访问数据时，都会调用<a href="https://github.com/antirez/redis/blob/unstable/src/db.c#L55" target="_blank" rel="noopener"><code>lookupKey</code></a>方法</p>
|
|
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/* Low level key lookup API, not actually called directly from commands</span></span><br><span class="line"><span class="comment"> * implementations that should instead rely on lookupKeyRead(),</span></span><br><span class="line"><span class="comment"> * lookupKeyWrite() and lookupKeyReadWithFlags(). */</span></span><br><span class="line"><span class="function">robj *<span class="title">lookupKey</span><span class="params">(redisDb *db, robj *key, <span class="keyword">int</span> flags)</span> </span>{</span><br><span class="line"> dictEntry *de = dictFind(db->dict,key->ptr);</span><br><span class="line"> <span class="keyword">if</span> (de) {</span><br><span class="line"> robj *val = dictGetVal(de);</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* Update the access time for the ageing algorithm.</span></span><br><span class="line"><span class="comment"> * Don't do it if we have a saving child, as this will trigger</span></span><br><span class="line"><span class="comment"> * a copy on write madness. */</span></span><br><span class="line"> <span class="keyword">if</span> (!hasActiveChildProcess() && !(flags & LOOKUP_NOTOUCH)){</span><br><span class="line"> <span class="keyword">if</span> (server.maxmemory_policy & MAXMEMORY_FLAG_LFU) {</span><br><span class="line"> <span class="comment">// 这个是后面一节的内容</span></span><br><span class="line"> updateLFU(val);</span><br><span class="line"> } <span class="keyword">else</span> {</span><br><span class="line"> <span class="comment">// 对于这个分支，访问时就会去更新 lru 值</span></span><br><span class="line"> val->lru = LRU_CLOCK();</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line"> <span class="keyword">return</span> val;</span><br><span class="line"> } <span class="keyword">else</span> {</span><br><span class="line"> <span class="keyword">return</span> <span class="literal">NULL</span>;</span><br><span class="line"> }</span><br><span class="line">}</span><br><span class="line"><span class="comment">/* This function is used to obtain the current LRU clock.</span></span><br><span class="line"><span class="comment"> * If the current resolution is lower than the frequency we refresh the</span></span><br><span class="line"><span class="comment"> * LRU clock (as it should be in production servers) we return the</span></span><br><span class="line"><span class="comment"> * precomputed value, otherwise we need to resort to a system call. */</span></span><br><span class="line"><span class="function"><span class="keyword">unsigned</span> <span class="keyword">int</span> <span class="title">LRU_CLOCK</span><span class="params">(<span class="keyword">void</span>)</span> </span>{</span><br><span class="line"> <span class="keyword">unsigned</span> <span class="keyword">int</span> lruclock;</span><br><span class="line"> <span class="keyword">if</span> (<span class="number">1000</span>/server.hz <= LRU_CLOCK_RESOLUTION) {</span><br><span class="line"> <span class="comment">// 如果服务器的频率server.hz大于 1 时就是用系统预设的 lruclock</span></span><br><span class="line"> lruclock = server.lruclock;</span><br><span class="line"> } <span class="keyword">else</span> {</span><br><span class="line"> lruclock = getLRUClock();</span><br><span class="line"> }</span><br><span class="line"> <span class="keyword">return</span> lruclock;</span><br><span class="line">}</span><br><span class="line"><span class="comment">/* Return the LRU clock, based on the clock resolution. This is a time</span></span><br><span class="line"><span class="comment"> * in a reduced-bits format that can be used to set and check the</span></span><br><span class="line"><span class="comment"> * object->lru field of redisObject structures. */</span></span><br><span class="line"><span class="function"><span class="keyword">unsigned</span> <span class="keyword">int</span> <span class="title">getLRUClock</span><span class="params">(<span class="keyword">void</span>)</span> </span>{</span><br><span class="line"> <span class="keyword">return</span> (mstime()/LRU_CLOCK_RESOLUTION) & LRU_CLOCK_MAX;</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
|
|
<p>redis 处理命令是在这里<a href="https://github.com/antirez/redis/blob/unstable/src/server.c#L3355" target="_blank" rel="noopener"><code>processCommand</code></a></p>
|
|
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/* If this function gets called we already read a whole</span></span><br><span class="line"><span class="comment"> * command, arguments are in the client argv/argc fields.</span></span><br><span class="line"><span class="comment"> * processCommand() execute the command or prepare the</span></span><br><span class="line"><span class="comment"> * server for a bulk read from the client.</span></span><br><span class="line"><span class="comment"> *</span></span><br><span class="line"><span class="comment"> * If C_OK is returned the client is still alive and valid and</span></span><br><span class="line"><span class="comment"> * other operations can be performed by the caller. Otherwise</span></span><br><span class="line"><span class="comment"> * if C_ERR is returned the client was destroyed (i.e. after QUIT). */</span></span><br><span class="line"><span class="function"><span class="keyword">int</span> <span class="title">processCommand</span><span class="params">(client *c)</span> </span>{</span><br><span class="line"> moduleCallCommandFilters(c);</span><br><span class="line"></span><br><span class="line"> </span><br><span class="line"></span><br><span class="line"> <span class="comment">/* Handle the maxmemory directive.</span></span><br><span class="line"><span class="comment"> *</span></span><br><span class="line"><span class="comment"> * Note that we do not want to reclaim memory if we are here re-entering</span></span><br><span class="line"><span class="comment"> * the event loop since there is a busy Lua script running in timeout</span></span><br><span class="line"><span class="comment"> * condition, to avoid mixing the propagation of scripts with the</span></span><br><span class="line"><span class="comment"> * propagation of DELs due to eviction. */</span></span><br><span class="line"> <span class="keyword">if</span> (server.maxmemory && !server.lua_timedout) {</span><br><span class="line"> <span class="keyword">int</span> out_of_memory = freeMemoryIfNeededAndSafe() == C_ERR;</span><br><span class="line"> <span class="comment">/* freeMemoryIfNeeded may flush slave output buffers. This may result</span></span><br><span class="line"><span class="comment"> * into a slave, that may be the active client, to be freed. */</span></span><br><span class="line"> <span class="keyword">if</span> (server.current_client == <span class="literal">NULL</span>) <span class="keyword">return</span> C_ERR;</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* It was impossible to free enough memory, and the command the client</span></span><br><span class="line"><span class="comment"> * is trying to execute is denied during OOM conditions or the client</span></span><br><span class="line"><span class="comment"> * is in MULTI/EXEC context? Error. */</span></span><br><span class="line"> <span class="keyword">if</span> (out_of_memory &&</span><br><span class="line"> (c->cmd->flags & CMD_DENYOOM ||</span><br><span class="line"> (c->flags & CLIENT_MULTI &&</span><br><span class="line"> c->cmd->proc != execCommand &&</span><br><span class="line"> c->cmd->proc != discardCommand)))</span><br><span class="line"> {</span><br><span class="line"> flagTransaction(c);</span><br><span class="line"> addReply(c, shared.oomerr);</span><br><span class="line"> <span class="keyword">return</span> C_OK;</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
|
|
<p>这里只摘了部分，当需要清理内存时就会调用, 然后调用了<a href="https://github.com/antirez/redis/blob/unstable/src/evict.c#L631" target="_blank" rel="noopener"><code>freeMemoryIfNeededAndSafe</code></a></p>
|
|
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br><span class="line">49</span><br><span class="line">50</span><br><span class="line">51</span><br><span class="line">52</span><br><span class="line">53</span><br><span class="line">54</span><br><span class="line">55</span><br><span class="line">56</span><br><span class="line">57</span><br><span class="line">58</span><br><span class="line">59</span><br><span class="line">60</span><br><span class="line">61</span><br><span class="line">62</span><br><span class="line">63</span><br><span class="line">64</span><br><span class="line">65</span><br><span class="line">66</span><br><span class="line">67</span><br><span class="line">68</span><br><span class="line">69</span><br><span class="line">70</span><br><span class="line">71</span><br><span class="line">72</span><br><span class="line">73</span><br><span class="line">74</span><br><span class="line">75</span><br><span class="line">76</span><br><span class="line">77</span><br><span class="line">78</span><br><span class="line">79</span><br><span class="line">80</span><br><span class="line">81</span><br><span class="line">82</span><br><span class="line">83</span><br><span class="line">84</span><br><span class="line">85</span><br><span class="line">86</span><br><span class="line">87</span><br><span class="line">88</span><br><span class="line">89</span><br><span class="line">90</span><br><span class="line">91</span><br><span class="line">92</span><br><span class="line">93</span><br><span class="line">94</span><br><span class="line">95</span><br><span class="line">96</span><br><span class="line">97</span><br><span class="line">98</span><br><span class="line">99</span><br><span class="line">100</span><br><span class="line">101</span><br><span class="line">102</span><br><span class="line">103</span><br><span class="line">104</span><br><span class="line">105</span><br><span class="line">106</span><br><span class="line">107</span><br><span class="line">108</span><br><span class="line">109</span><br><span class="line">110</span><br><span class="line">111</span><br><span class="line">112</span><br><span class="line">113</span><br><span class="line">114</span><br><span class="line">115</span><br><span class="line">116</span><br><span class="line">117</span><br><span class="line">118</span><br><span class="line">119</span><br><span class="line">120</span><br><span class="line">121</span><br><span class="line">122</span><br><span class="line">123</span><br><span class="line">124</span><br><span class="line">125</span><br><span class="line">126</span><br><span class="line">127</span><br><span class="line">128</span><br><span class="line">129</span><br><span class="line">130</span><br><span class="line">131</span><br><span class="line">132</span><br><span class="line">133</span><br><span class="line">134</span><br><span class="line">135</span><br><span class="line">136</span><br><span class="line">137</span><br><span class="line">138</span><br><span class="line">139</span><br><span class="line">140</span><br><span class="line">141</span><br><span class="line">142</span><br><span class="line">143</span><br><span class="line">144</span><br><span class="line">145</span><br><span class="line">146</span><br><span class="line">147</span><br><span class="line">148</span><br><span class="line">149</span><br><span class="line">150</span><br><span class="line">151</span><br><span class="line">152</span><br><span class="line">153</span><br><span class="line">154</span><br><span class="line">155</span><br><span class="line">156</span><br><span class="line">157</span><br><span class="line">158</span><br><span class="line">159</span><br><span class="line">160</span><br><span class="line">161</span><br><span class="line">162</span><br><span class="line">163</span><br><span class="line">164</span><br><span class="line">165</span><br><span class="line">166</span><br><span class="line">167</span><br><span class="line">168</span><br><span class="line">169</span><br><span class="line">170</span><br><span class="line">171</span><br><span class="line">172</span><br><span class="line">173</span><br><span class="line">174</span><br><span class="line">175</span><br><span class="line">176</span><br><span class="line">177</span><br><span class="line">178</span><br><span class="line">179</span><br><span class="line">180</span><br><span class="line">181</span><br><span class="line">182</span><br><span class="line">183</span><br><span class="line">184</span><br><span class="line">185</span><br><span class="line">186</span><br><span class="line">187</span><br><span class="line">188</span><br><span class="line">189</span><br><span class="line">190</span><br><span class="line">191</span><br><span class="line">192</span><br><span class="line">193</span><br><span class="line">194</span><br><span class="line">195</span><br><span class="line">196</span><br><span class="line">197</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/* This is a wrapper for freeMemoryIfNeeded() that only really calls the</span></span><br><span class="line"><span class="comment"> * function if right now there are the conditions to do so safely:</span></span><br><span class="line"><span class="comment"> *</span></span><br><span class="line"><span class="comment"> * - There must be no script in timeout condition.</span></span><br><span class="line"><span class="comment"> * - Nor we are loading data right now.</span></span><br><span class="line"><span class="comment"> *</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"><span class="function"><span class="keyword">int</span> <span class="title">freeMemoryIfNeededAndSafe</span><span class="params">(<span class="keyword">void</span>)</span> </span>{</span><br><span class="line"> <span class="keyword">if</span> (server.lua_timedout || server.loading) <span class="keyword">return</span> C_OK;</span><br><span class="line"> <span class="keyword">return</span> freeMemoryIfNeeded();</span><br><span class="line">}</span><br><span class="line"><span class="comment">/* This function is periodically called to see if there is memory to free</span></span><br><span class="line"><span class="comment"> * according to the current "maxmemory" settings. In case we are over the</span></span><br><span class="line"><span class="comment"> * memory limit, the function will try to free some memory to return back</span></span><br><span class="line"><span class="comment"> * under the limit.</span></span><br><span class="line"><span class="comment"> *</span></span><br><span class="line"><span class="comment"> * The function returns C_OK if we are under the memory limit or if we</span></span><br><span class="line"><span class="comment"> * were over the limit, but the attempt to free memory was successful.</span></span><br><span class="line"><span class="comment"> * Otehrwise if we are over the memory limit, but not enough memory</span></span><br><span class="line"><span class="comment"> * was freed to return back under the limit, the function returns C_ERR. */</span></span><br><span class="line"><span class="function"><span class="keyword">int</span> <span class="title">freeMemoryIfNeeded</span><span class="params">(<span class="keyword">void</span>)</span> </span>{</span><br><span class="line"> <span class="keyword">int</span> keys_freed = <span class="number">0</span>;</span><br><span class="line"> <span class="comment">/* By default replicas should ignore maxmemory</span></span><br><span class="line"><span class="comment"> * and just be masters exact copies. */</span></span><br><span class="line"> <span class="keyword">if</span> (server.masterhost && server.repl_slave_ignore_maxmemory) <span class="keyword">return</span> C_OK;</span><br><span class="line"></span><br><span class="line"> <span class="keyword">size_t</span> mem_reported, mem_tofree, mem_freed;</span><br><span class="line"> <span class="keyword">mstime_t</span> latency, eviction_latency;</span><br><span class="line"> <span class="keyword">long</span> <span class="keyword">long</span> delta;</span><br><span class="line"> <span class="keyword">int</span> slaves = listLength(server.slaves);</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* When clients are paused the dataset should be static not just from the</span></span><br><span class="line"><span class="comment"> * POV of clients not being able to write, but also from the POV of</span></span><br><span class="line"><span class="comment"> * expires and evictions of keys not being performed. */</span></span><br><span class="line"> <span class="keyword">if</span> (clientsArePaused()) <span class="keyword">return</span> C_OK;</span><br><span class="line"> <span class="keyword">if</span> (getMaxmemoryState(&mem_reported,<span class="literal">NULL</span>,&mem_tofree,<span class="literal">NULL</span>) == C_OK)</span><br><span class="line"> <span class="keyword">return</span> C_OK;</span><br><span class="line"></span><br><span class="line"> mem_freed = <span class="number">0</span>;</span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> (server.maxmemory_policy == MAXMEMORY_NO_EVICTION)</span><br><span class="line"> <span class="keyword">goto</span> cant_free; <span class="comment">/* We need to free memory, but policy forbids. */</span></span><br><span class="line"></span><br><span class="line"> latencyStartMonitor(latency);</span><br><span class="line"> <span class="keyword">while</span> (mem_freed < mem_tofree) {</span><br><span class="line"> <span class="keyword">int</span> j, k, i;</span><br><span class="line"> <span class="keyword">static</span> <span class="keyword">unsigned</span> <span class="keyword">int</span> next_db = <span class="number">0</span>;</span><br><span class="line"> sds bestkey = <span class="literal">NULL</span>;</span><br><span class="line"> <span class="keyword">int</span> bestdbid;</span><br><span class="line"> redisDb *db;</span><br><span class="line"> dict *dict;</span><br><span class="line"> dictEntry *de;</span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> (server.maxmemory_policy & (MAXMEMORY_FLAG_LRU|MAXMEMORY_FLAG_LFU) ||</span><br><span class="line"> server.maxmemory_policy == MAXMEMORY_VOLATILE_TTL)</span><br><span class="line"> {</span><br><span class="line"> <span class="class"><span class="keyword">struct</span> <span class="title">evictionPoolEntry</span> *<span class="title">pool</span> = <span class="title">EvictionPoolLRU</span>;</span></span><br><span class="line"></span><br><span class="line"> <span class="keyword">while</span>(bestkey == <span class="literal">NULL</span>) {</span><br><span class="line"> <span class="keyword">unsigned</span> <span class="keyword">long</span> total_keys = <span class="number">0</span>, keys;</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* We don't want to make local-db choices when expiring keys,</span></span><br><span class="line"><span class="comment"> * so to start populate the eviction pool sampling keys from</span></span><br><span class="line"><span class="comment"> * every DB. */</span></span><br><span class="line"> <span class="keyword">for</span> (i = <span class="number">0</span>; i < server.dbnum; i++) {</span><br><span class="line"> db = server.db+i;</span><br><span class="line"> dict = (server.maxmemory_policy & MAXMEMORY_FLAG_ALLKEYS) ?</span><br><span class="line"> db->dict : db->expires;</span><br><span class="line"> <span class="keyword">if</span> ((keys = dictSize(dict)) != <span class="number">0</span>) {</span><br><span class="line"> evictionPoolPopulate(i, dict, db->dict, pool);</span><br><span class="line"> total_keys += keys;</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line"> <span class="keyword">if</span> (!total_keys) <span class="keyword">break</span>; <span class="comment">/* No keys to evict. */</span></span><br><span class="line"></span><br><span class="line"> <span class="comment">/* Go backward from best to worst element to evict. */</span></span><br><span class="line"> <span class="keyword">for</span> (k = EVPOOL_SIZE<span class="number">-1</span>; k >= <span class="number">0</span>; k--) {</span><br><span class="line"> <span class="keyword">if</span> (pool[k].key == <span class="literal">NULL</span>) <span class="keyword">continue</span>;</span><br><span class="line"> bestdbid = pool[k].dbid;</span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> (server.maxmemory_policy & MAXMEMORY_FLAG_ALLKEYS) {</span><br><span class="line"> de = dictFind(server.db[pool[k].dbid].dict,</span><br><span class="line"> pool[k].key);</span><br><span class="line"> } <span class="keyword">else</span> {</span><br><span class="line"> de = dictFind(server.db[pool[k].dbid].expires,</span><br><span class="line"> pool[k].key);</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* Remove the entry from the pool. */</span></span><br><span class="line"> <span class="keyword">if</span> (pool[k].key != pool[k].cached)</span><br><span class="line"> sdsfree(pool[k].key);</span><br><span class="line"> pool[k].key = <span class="literal">NULL</span>;</span><br><span class="line"> pool[k].idle = <span class="number">0</span>;</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* If the key exists, is our pick. Otherwise it is</span></span><br><span class="line"><span class="comment"> * a ghost and we need to try the next element. */</span></span><br><span class="line"> <span class="keyword">if</span> (de) {</span><br><span class="line"> bestkey = dictGetKey(de);</span><br><span class="line"> <span class="keyword">break</span>;</span><br><span class="line"> } <span class="keyword">else</span> {</span><br><span class="line"> <span class="comment">/* Ghost... Iterate again. */</span></span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* volatile-random and allkeys-random policy */</span></span><br><span class="line"> <span class="keyword">else</span> <span class="keyword">if</span> (server.maxmemory_policy == MAXMEMORY_ALLKEYS_RANDOM ||</span><br><span class="line"> server.maxmemory_policy == MAXMEMORY_VOLATILE_RANDOM)</span><br><span class="line"> {</span><br><span class="line"> <span class="comment">/* When evicting a random key, we try to evict a key for</span></span><br><span class="line"><span class="comment"> * each DB, so we use the static 'next_db' variable to</span></span><br><span class="line"><span class="comment"> * incrementally visit all DBs. */</span></span><br><span class="line"> <span class="keyword">for</span> (i = <span class="number">0</span>; i < server.dbnum; i++) {</span><br><span class="line"> j = (++next_db) % server.dbnum;</span><br><span class="line"> db = server.db+j;</span><br><span class="line"> dict = (server.maxmemory_policy == MAXMEMORY_ALLKEYS_RANDOM) ?</span><br><span class="line"> db->dict : db->expires;</span><br><span class="line"> <span class="keyword">if</span> (dictSize(dict) != <span class="number">0</span>) {</span><br><span class="line"> de = dictGetRandomKey(dict);</span><br><span class="line"> bestkey = dictGetKey(de);</span><br><span class="line"> bestdbid = j;</span><br><span class="line"> <span class="keyword">break</span>;</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* Finally remove the selected key. */</span></span><br><span class="line"> <span class="keyword">if</span> (bestkey) {</span><br><span class="line"> db = server.db+bestdbid;</span><br><span class="line"> robj *keyobj = createStringObject(bestkey,sdslen(bestkey));</span><br><span class="line"> propagateExpire(db,keyobj,server.lazyfree_lazy_eviction);</span><br><span class="line"> <span class="comment">/* We compute the amount of memory freed by db*Delete() alone.</span></span><br><span class="line"><span class="comment"> * It is possible that actually the memory needed to propagate</span></span><br><span class="line"><span class="comment"> * the DEL in AOF and replication link is greater than the one</span></span><br><span class="line"><span class="comment"> * we are freeing removing the key, but we can't account for</span></span><br><span class="line"><span class="comment"> * that otherwise we would never exit the loop.</span></span><br><span class="line"><span class="comment"> *</span></span><br><span class="line"><span class="comment"> * AOF and Output buffer memory will be freed eventually so</span></span><br><span class="line"><span class="comment"> * we only care about memory used by the key space. */</span></span><br><span class="line"> delta = (<span class="keyword">long</span> <span class="keyword">long</span>) zmalloc_used_memory();</span><br><span class="line"> latencyStartMonitor(eviction_latency);</span><br><span class="line"> <span class="keyword">if</span> (server.lazyfree_lazy_eviction)</span><br><span class="line"> dbAsyncDelete(db,keyobj);</span><br><span class="line"> <span class="keyword">else</span></span><br><span class="line"> dbSyncDelete(db,keyobj);</span><br><span class="line"> latencyEndMonitor(eviction_latency);</span><br><span class="line"> latencyAddSampleIfNeeded(<span class="string">"eviction-del"</span>,eviction_latency);</span><br><span class="line"> latencyRemoveNestedEvent(latency,eviction_latency);</span><br><span class="line"> delta -= (<span class="keyword">long</span> <span class="keyword">long</span>) zmalloc_used_memory();</span><br><span class="line"> mem_freed += delta;</span><br><span class="line"> server.stat_evictedkeys++;</span><br><span class="line"> notifyKeyspaceEvent(NOTIFY_EVICTED, <span class="string">"evicted"</span>,</span><br><span class="line"> keyobj, db->id);</span><br><span class="line"> decrRefCount(keyobj);</span><br><span class="line"> keys_freed++;</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* When the memory to free starts to be big enough, we may</span></span><br><span class="line"><span class="comment"> * start spending so much time here that is impossible to</span></span><br><span class="line"><span class="comment"> * deliver data to the slaves fast enough, so we force the</span></span><br><span class="line"><span class="comment"> * transmission here inside the loop. */</span></span><br><span class="line"> <span class="keyword">if</span> (slaves) flushSlavesOutputBuffers();</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* Normally our stop condition is the ability to release</span></span><br><span class="line"><span class="comment"> * a fixed, pre-computed amount of memory. However when we</span></span><br><span class="line"><span class="comment"> * are deleting objects in another thread, it's better to</span></span><br><span class="line"><span class="comment"> * check, from time to time, if we already reached our target</span></span><br><span class="line"><span class="comment"> * memory, since the "mem_freed" amount is computed only</span></span><br><span class="line"><span class="comment"> * across the dbAsyncDelete() call, while the thread can</span></span><br><span class="line"><span class="comment"> * release the memory all the time. */</span></span><br><span class="line"> <span class="keyword">if</span> (server.lazyfree_lazy_eviction && !(keys_freed % <span class="number">16</span>)) {</span><br><span class="line"> <span class="keyword">if</span> (getMaxmemoryState(<span class="literal">NULL</span>,<span class="literal">NULL</span>,<span class="literal">NULL</span>,<span class="literal">NULL</span>) == C_OK) {</span><br><span class="line"> <span class="comment">/* Let's satisfy our stop condition. */</span></span><br><span class="line"> mem_freed = mem_tofree;</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line"> } <span class="keyword">else</span> {</span><br><span class="line"> latencyEndMonitor(latency);</span><br><span class="line"> latencyAddSampleIfNeeded(<span class="string">"eviction-cycle"</span>,latency);</span><br><span class="line"> <span class="keyword">goto</span> cant_free; <span class="comment">/* nothing to free... */</span></span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line"> latencyEndMonitor(latency);</span><br><span class="line"> latencyAddSampleIfNeeded(<span class="string">"eviction-cycle"</span>,latency);</span><br><span class="line"> <span class="keyword">return</span> C_OK;</span><br><span class="line"></span><br><span class="line">cant_free:</span><br><span class="line"> <span class="comment">/* We are here if we are not able to reclaim memory. There is only one</span></span><br><span class="line"><span class="comment"> * last thing we can try: check if the lazyfree thread has jobs in queue</span></span><br><span class="line"><span class="comment"> * and wait... */</span></span><br><span class="line"> <span class="keyword">while</span>(bioPendingJobsOfType(BIO_LAZY_FREE)) {</span><br><span class="line"> <span class="keyword">if</span> (((mem_reported - zmalloc_used_memory()) + mem_freed) >= mem_tofree)</span><br><span class="line"> <span class="keyword">break</span>;</span><br><span class="line"> usleep(<span class="number">1000</span>);</span><br><span class="line"> }</span><br><span class="line"> <span class="keyword">return</span> C_ERR;</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
|
|
<p>这里就是根据具体策略去淘汰 key，首先是要往 pool 更新 key，更新key 的方法是<a href="https://github.com/antirez/redis/blob/unstable/src/evict.c#L162" target="_blank" rel="noopener"><code>evictionPoolPopulate</code></a></p>
|
|
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br><span class="line">49</span><br><span class="line">50</span><br><span class="line">51</span><br><span class="line">52</span><br><span class="line">53</span><br><span class="line">54</span><br><span class="line">55</span><br><span class="line">56</span><br><span class="line">57</span><br><span class="line">58</span><br><span class="line">59</span><br><span class="line">60</span><br><span class="line">61</span><br><span class="line">62</span><br><span class="line">63</span><br><span class="line">64</span><br><span class="line">65</span><br><span class="line">66</span><br><span class="line">67</span><br><span class="line">68</span><br><span class="line">69</span><br><span class="line">70</span><br><span class="line">71</span><br><span class="line">72</span><br><span class="line">73</span><br><span class="line">74</span><br><span class="line">75</span><br><span class="line">76</span><br><span class="line">77</span><br><span class="line">78</span><br><span class="line">79</span><br><span class="line">80</span><br><span class="line">81</span><br><span class="line">82</span><br><span class="line">83</span><br><span class="line">84</span><br><span class="line">85</span><br><span class="line">86</span><br><span class="line">87</span><br><span class="line">88</span><br><span class="line">89</span><br><span class="line">90</span><br><span class="line">91</span><br><span class="line">92</span><br><span class="line">93</span><br><span class="line">94</span><br><span class="line">95</span><br><span class="line">96</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">void</span> <span class="title">evictionPoolPopulate</span><span class="params">(<span class="keyword">int</span> dbid, dict *sampledict, dict *keydict, struct evictionPoolEntry *pool)</span> </span>{</span><br><span class="line"> <span class="keyword">int</span> j, k, count;</span><br><span class="line"> dictEntry *samples[server.maxmemory_samples];</span><br><span class="line"></span><br><span class="line"> count = dictGetSomeKeys(sampledict,samples,server.maxmemory_samples);</span><br><span class="line"> <span class="keyword">for</span> (j = <span class="number">0</span>; j < count; j++) {</span><br><span class="line"> <span class="keyword">unsigned</span> <span class="keyword">long</span> <span class="keyword">long</span> idle;</span><br><span class="line"> sds key;</span><br><span class="line"> robj *o;</span><br><span class="line"> dictEntry *de;</span><br><span class="line"></span><br><span class="line"> de = samples[j];</span><br><span class="line"> key = dictGetKey(de);</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* If the dictionary we are sampling from is not the main</span></span><br><span class="line"><span class="comment"> * dictionary (but the expires one) we need to lookup the key</span></span><br><span class="line"><span class="comment"> * again in the key dictionary to obtain the value object. */</span></span><br><span class="line"> <span class="keyword">if</span> (server.maxmemory_policy != MAXMEMORY_VOLATILE_TTL) {</span><br><span class="line"> <span class="keyword">if</span> (sampledict != keydict) de = dictFind(keydict, key);</span><br><span class="line"> o = dictGetVal(de);</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* Calculate the idle time according to the policy. This is called</span></span><br><span class="line"><span class="comment"> * idle just because the code initially handled LRU, but is in fact</span></span><br><span class="line"><span class="comment"> * just a score where an higher score means better candidate. */</span></span><br><span class="line"> <span class="keyword">if</span> (server.maxmemory_policy & MAXMEMORY_FLAG_LRU) {</span><br><span class="line"> idle = estimateObjectIdleTime(o);</span><br><span class="line"> } <span class="keyword">else</span> <span class="keyword">if</span> (server.maxmemory_policy & MAXMEMORY_FLAG_LFU) {</span><br><span class="line"> <span class="comment">/* When we use an LRU policy, we sort the keys by idle time</span></span><br><span class="line"><span class="comment"> * so that we expire keys starting from greater idle time.</span></span><br><span class="line"><span class="comment"> * However when the policy is an LFU one, we have a frequency</span></span><br><span class="line"><span class="comment"> * estimation, and we want to evict keys with lower frequency</span></span><br><span class="line"><span class="comment"> * first. So inside the pool we put objects using the inverted</span></span><br><span class="line"><span class="comment"> * frequency subtracting the actual frequency to the maximum</span></span><br><span class="line"><span class="comment"> * frequency of 255. */</span></span><br><span class="line"> idle = <span class="number">255</span>-LFUDecrAndReturn(o);</span><br><span class="line"> } <span class="keyword">else</span> <span class="keyword">if</span> (server.maxmemory_policy == MAXMEMORY_VOLATILE_TTL) {</span><br><span class="line"> <span class="comment">/* In this case the sooner the expire the better. */</span></span><br><span class="line"> idle = ULLONG_MAX - (<span class="keyword">long</span>)dictGetVal(de);</span><br><span class="line"> } <span class="keyword">else</span> {</span><br><span class="line"> serverPanic(<span class="string">"Unknown eviction policy in evictionPoolPopulate()"</span>);</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* Insert the element inside the pool.</span></span><br><span class="line"><span class="comment"> * First, find the first empty bucket or the first populated</span></span><br><span class="line"><span class="comment"> * bucket that has an idle time smaller than our idle time. */</span></span><br><span class="line"> k = <span class="number">0</span>;</span><br><span class="line"> <span class="keyword">while</span> (k < EVPOOL_SIZE &&</span><br><span class="line"> pool[k].key &&</span><br><span class="line"> pool[k].idle < idle) k++;</span><br><span class="line"> <span class="keyword">if</span> (k == <span class="number">0</span> && pool[EVPOOL_SIZE<span class="number">-1</span>].key != <span class="literal">NULL</span>) {</span><br><span class="line"> <span class="comment">/* Can't insert if the element is < the worst element we have</span></span><br><span class="line"><span class="comment"> * and there are no empty buckets. */</span></span><br><span class="line"> <span class="keyword">continue</span>;</span><br><span class="line"> } <span class="keyword">else</span> <span class="keyword">if</span> (k < EVPOOL_SIZE && pool[k].key == <span class="literal">NULL</span>) {</span><br><span class="line"> <span class="comment">/* Inserting into empty position. No setup needed before insert. */</span></span><br><span class="line"> } <span class="keyword">else</span> {</span><br><span class="line"> <span class="comment">/* Inserting in the middle. Now k points to the first element</span></span><br><span class="line"><span class="comment"> * greater than the element to insert. */</span></span><br><span class="line"> <span class="keyword">if</span> (pool[EVPOOL_SIZE<span class="number">-1</span>].key == <span class="literal">NULL</span>) {</span><br><span class="line"> <span class="comment">/* Free space on the right? Insert at k shifting</span></span><br><span class="line"><span class="comment"> * all the elements from k to end to the right. */</span></span><br><span class="line"></span><br><span class="line"> <span class="comment">/* Save SDS before overwriting. */</span></span><br><span class="line"> sds cached = pool[EVPOOL_SIZE<span class="number">-1</span>].cached;</span><br><span class="line"> memmove(pool+k+<span class="number">1</span>,pool+k,</span><br><span class="line"> <span class="keyword">sizeof</span>(pool[<span class="number">0</span>])*(EVPOOL_SIZE-k<span class="number">-1</span>));</span><br><span class="line"> pool[k].cached = cached;</span><br><span class="line"> } <span class="keyword">else</span> {</span><br><span class="line"> <span class="comment">/* No free space on right? Insert at k-1 */</span></span><br><span class="line"> k--;</span><br><span class="line"> <span class="comment">/* Shift all elements on the left of k (included) to the</span></span><br><span class="line"><span class="comment"> * left, so we discard the element with smaller idle time. */</span></span><br><span class="line"> sds cached = pool[<span class="number">0</span>].cached; <span class="comment">/* Save SDS before overwriting. */</span></span><br><span class="line"> <span class="keyword">if</span> (pool[<span class="number">0</span>].key != pool[<span class="number">0</span>].cached) sdsfree(pool[<span class="number">0</span>].key);</span><br><span class="line"> memmove(pool,pool+<span class="number">1</span>,<span class="keyword">sizeof</span>(pool[<span class="number">0</span>])*k);</span><br><span class="line"> pool[k].cached = cached;</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* Try to reuse the cached SDS string allocated in the pool entry,</span></span><br><span class="line"><span class="comment"> * because allocating and deallocating this object is costly</span></span><br><span class="line"><span class="comment"> * (according to the profiler, not my fantasy. Remember:</span></span><br><span class="line"><span class="comment"> * premature optimizbla bla bla bla. */</span></span><br><span class="line"> <span class="keyword">int</span> klen = sdslen(key);</span><br><span class="line"> <span class="keyword">if</span> (klen > EVPOOL_CACHED_SDS_SIZE) {</span><br><span class="line"> pool[k].key = sdsdup(key);</span><br><span class="line"> } <span class="keyword">else</span> {</span><br><span class="line"> <span class="built_in">memcpy</span>(pool[k].cached,key,klen+<span class="number">1</span>);</span><br><span class="line"> sdssetlen(pool[k].cached,klen);</span><br><span class="line"> pool[k].key = pool[k].cached;</span><br><span class="line"> }</span><br><span class="line"> pool[k].idle = idle;</span><br><span class="line"> pool[k].dbid = dbid;</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
|
|
<p><code>Redis</code>随机选择<code>maxmemory_samples</code>数量的key，然后计算这些<code>key</code>的空闲时间<code>idle time</code>，当满足条件时(比pool中的某些键的空闲时间还大)就可以进<code>pool</code>。<code>pool</code>更新之后，就淘汰<code>pool</code>中空闲时间最大的键。</p>
|
|
<p><a href="https://github.com/antirez/redis/blob/unstable/src/evict.c#L90" target="_blank" rel="noopener"><code>estimateObjectIdleTime</code></a>用来计算Redis对象的空闲时间：</p>
|
|
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/* Given an object returns the min number of milliseconds the object was never</span></span><br><span class="line"><span class="comment"> * requested, using an approximated LRU algorithm. */</span></span><br><span class="line"><span class="function"><span class="keyword">unsigned</span> <span class="keyword">long</span> <span class="keyword">long</span> <span class="title">estimateObjectIdleTime</span><span class="params">(robj *o)</span> </span>{</span><br><span class="line"> <span class="keyword">unsigned</span> <span class="keyword">long</span> <span class="keyword">long</span> lruclock = LRU_CLOCK();</span><br><span class="line"> <span class="keyword">if</span> (lruclock >= o->lru) {</span><br><span class="line"> <span class="keyword">return</span> (lruclock - o->lru) * LRU_CLOCK_RESOLUTION;</span><br><span class="line"> } <span class="keyword">else</span> {</span><br><span class="line"> <span class="keyword">return</span> (lruclock + (LRU_CLOCK_MAX - o->lru)) *</span><br><span class="line"> LRU_CLOCK_RESOLUTION;</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
|
|
<p>空闲时间第一种是 lurclock 大于对象的 lru，那么就是减一下乘以精度，因为 lruclock 有可能是已经预生成的，所以会可能走下面这个</p>
|
|
<h3 id="LFU"><a href="#LFU" class="headerlink" title="LFU"></a>LFU</h3><p>上面介绍了LRU 的算法，但是考虑一种场景</p>
|
|
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line">~~~~~A~~~~~A~~~~~A~~~~A~~~~~A~~~~~A~~|</span><br><span class="line">~~B~~B~~B~~B~~B~~B~~B~~B~~B~~B~~B~~B~|</span><br><span class="line">~~~~~~~~~~C~~~~~~~~~C~~~~~~~~~C~~~~~~|</span><br><span class="line">~~~~~D~~~~~~~~~~D~~~~~~~~~D~~~~~~~~~D|</span><br></pre></td></tr></table></figure>
|
|
<p>可以发现，当采用 lru 的淘汰策略的时候，D 是最新的，会被认为是最值得保留的，但是事实上还不如 A 跟 B，然后 antirez 大神就想到了LFU (Least Frequently Used) 这个算法, 显然对于上面的四个 key 的访问频率，保留优先级应该是 B > A > C = D<br>那要怎么来实现这个 LFU 算法呢，其实像LRU，理想的情况就是维护个链表，把最新访问的放到头上去，但是这个会影响访问速度，注意到前面代码的应该可以看到，redisObject 的 lru 字段其实是两用的，当策略是 LFU 时，这个字段就另作他用了，它的 24 位长度被分成两部分</p>
|
|
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line"> 16 bits 8 bits</span><br><span class="line">+----------------+--------+</span><br><span class="line">+ Last decr time | LOG_C |</span><br><span class="line">+----------------+--------+</span><br></pre></td></tr></table></figure>
|
|
<p>前16位字段是最后一次递减时间，因此Redis知道 上一次计数器递减，后8位是 计数器 counter。<br>LFU 的主体策略就是当这个 key 被访问的次数越多频率越高他就越容易被保留下来，并且是最近被访问的频率越高。这其实有两个事情要做，一个是在访问的时候增加计数值，在一定长时间不访问时进行衰减，所以这里用了两个值，前 16 位记录上一次衰减的时间，后 8 位记录具体的计数值。<br>Redis4.0之后为maxmemory_policy淘汰策略添加了两个LFU模式：</p>
|
|
<p><code>volatile-lfu</code>：对有过期时间的key采用LFU淘汰策略<br><code>allkeys-lfu</code>：对全部key采用LFU淘汰策略<br>还有2个配置可以调整LFU算法： </p>
|
|
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br></pre></td><td class="code"><pre><span class="line">lfu-log-factor 10</span><br><span class="line">lfu-decay-time 1</span><br><span class="line">``` </span><br><span class="line">`lfu-log-factor` 可以调整计数器counter的增长速度，lfu-log-factor越大，counter增长的越慢。</span><br><span class="line"></span><br><span class="line">`lfu-decay-time`是一个以分钟为单位的数值，可以调整counter的减少速度</span><br><span class="line">这里有个问题是 8 位大小够计么，访问一次加 1 的话的确不够，不过大神就是大神，才不会这么简单的加一。往下看代码</span><br><span class="line">```C</span><br><span class="line">/* Low level key lookup API, not actually called directly from commands</span><br><span class="line"> * implementations that should instead rely on lookupKeyRead(),</span><br><span class="line"> * lookupKeyWrite() and lookupKeyReadWithFlags(). */</span><br><span class="line">robj *lookupKey(redisDb *db, robj *key, int flags) {</span><br><span class="line"> dictEntry *de = dictFind(db->dict,key->ptr);</span><br><span class="line"> if (de) {</span><br><span class="line"> robj *val = dictGetVal(de);</span><br><span class="line"></span><br><span class="line"> /* Update the access time for the ageing algorithm.</span><br><span class="line"> * Don't do it if we have a saving child, as this will trigger</span><br><span class="line"> * a copy on write madness. */</span><br><span class="line"> if (!hasActiveChildProcess() && !(flags & LOOKUP_NOTOUCH)){</span><br><span class="line"> if (server.maxmemory_policy & MAXMEMORY_FLAG_LFU) {</span><br><span class="line"> // 当淘汰策略是 LFU 时，就会调用这个updateLFU</span><br><span class="line"> updateLFU(val);</span><br><span class="line"> } else {</span><br><span class="line"> val->lru = LRU_CLOCK();</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line"> return val;</span><br><span class="line"> } else {</span><br><span class="line"> return NULL;</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
|
|
<p><a href="https://github.com/antirez/redis/blob/unstable/src/db.c#L46" target="_blank" rel="noopener"><code>updateLFU</code></a> 这个其实个入口，调用了两个重要的方法</p>
|
|
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/* Update LFU when an object is accessed.</span></span><br><span class="line"><span class="comment"> * Firstly, decrement the counter if the decrement time is reached.</span></span><br><span class="line"><span class="comment"> * Then logarithmically increment the counter, and update the access time. */</span></span><br><span class="line"><span class="function"><span class="keyword">void</span> <span class="title">updateLFU</span><span class="params">(robj *val)</span> </span>{</span><br><span class="line"> <span class="keyword">unsigned</span> <span class="keyword">long</span> counter = LFUDecrAndReturn(val);</span><br><span class="line"> counter = LFULogIncr(counter);</span><br><span class="line"> val->lru = (LFUGetTimeInMinutes()<<<span class="number">8</span>) | counter;</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
|
|
<p>首先来看看<a href="https://github.com/antirez/redis/blob/unstable/src/evict.c#L335" target="_blank" rel="noopener"><code>LFUDecrAndReturn</code></a>，这个方法的作用是根据上一次衰减时间和系统配置的 <code>lfu-decay-time</code> 参数来确定需要将 counter 减去多少</p>
|
|
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/* If the object decrement time is reached decrement the LFU counter but</span></span><br><span class="line"><span class="comment"> * do not update LFU fields of the object, we update the access time</span></span><br><span class="line"><span class="comment"> * and counter in an explicit way when the object is really accessed.</span></span><br><span class="line"><span class="comment"> * And we will times halve the counter according to the times of</span></span><br><span class="line"><span class="comment"> * elapsed time than server.lfu_decay_time.</span></span><br><span class="line"><span class="comment"> * Return the object frequency counter.</span></span><br><span class="line"><span class="comment"> *</span></span><br><span class="line"><span class="comment"> * This function is used in order to scan the dataset for the best object</span></span><br><span class="line"><span class="comment"> * to fit: as we check for the candidate, we incrementally decrement the</span></span><br><span class="line"><span class="comment"> * counter of the scanned objects if needed. */</span></span><br><span class="line"><span class="function"><span class="keyword">unsigned</span> <span class="keyword">long</span> <span class="title">LFUDecrAndReturn</span><span class="params">(robj *o)</span> </span>{</span><br><span class="line"> <span class="comment">// 右移 8 位，拿到上次衰减时间</span></span><br><span class="line"> <span class="keyword">unsigned</span> <span class="keyword">long</span> ldt = o->lru >> <span class="number">8</span>;</span><br><span class="line"> <span class="comment">// 对 255 做与操作，拿到 counter 值</span></span><br><span class="line"> <span class="keyword">unsigned</span> <span class="keyword">long</span> counter = o->lru & <span class="number">255</span>;</span><br><span class="line"> <span class="comment">// 根据lfu_decay_time来算出过了多少个衰减周期</span></span><br><span class="line"> <span class="keyword">unsigned</span> <span class="keyword">long</span> num_periods = server.lfu_decay_time ? LFUTimeElapsed(ldt) / server.lfu_decay_time : <span class="number">0</span>;</span><br><span class="line"> <span class="keyword">if</span> (num_periods)</span><br><span class="line"> counter = (num_periods > counter) ? <span class="number">0</span> : counter - num_periods;</span><br><span class="line"> <span class="keyword">return</span> counter;</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
|
|
<p>然后是加，调用了<a href="https://github.com/antirez/redis/blob/unstable/src/evict.c#L315" target="_blank" rel="noopener"><code>LFULogIncr</code></a></p>
|
|
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/* Logarithmically increment a counter. The greater is the current counter value</span></span><br><span class="line"><span class="comment"> * the less likely is that it gets really implemented. Saturate it at 255. */</span></span><br><span class="line"><span class="function"><span class="keyword">uint8_t</span> <span class="title">LFULogIncr</span><span class="params">(<span class="keyword">uint8_t</span> counter)</span> </span>{</span><br><span class="line"> <span class="comment">// 最大值就是 255，到顶了就不加了</span></span><br><span class="line"> <span class="keyword">if</span> (counter == <span class="number">255</span>) <span class="keyword">return</span> <span class="number">255</span>;</span><br><span class="line"> <span class="comment">// 生成个随机小数</span></span><br><span class="line"> <span class="keyword">double</span> r = (<span class="keyword">double</span>)rand()/RAND_MAX;</span><br><span class="line"> <span class="comment">// 减去个基础值，LFU_INIT_VAL = 5，防止刚进来就被逐出</span></span><br><span class="line"> <span class="keyword">double</span> baseval = counter - LFU_INIT_VAL;</span><br><span class="line"> <span class="comment">// 如果是小于 0，</span></span><br><span class="line"> <span class="keyword">if</span> (baseval < <span class="number">0</span>) baseval = <span class="number">0</span>;</span><br><span class="line"> <span class="comment">// 如果 baseval 是 0，那么 p 就是 1了，后面 counter 直接加一，如果不是的话，得看系统参数lfu_log_factor，这个越大，除出来的 p 越小，那么 counter++的可能性也越小，这样子就把前面的疑问给解决了，不是直接+1 的</span></span><br><span class="line"> <span class="keyword">double</span> p = <span class="number">1.0</span>/(baseval*server.lfu_log_factor+<span class="number">1</span>);</span><br><span class="line"> <span class="keyword">if</span> (r < p) counter++;</span><br><span class="line"> <span class="keyword">return</span> counter;</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
|
|
<p>大概的变化速度可以参考</p>
|
|
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br></pre></td><td class="code"><pre><span class="line">+--------+------------+------------+------------+------------+------------+</span><br><span class="line">| factor | 100 hits | 1000 hits | 100K hits | 1M hits | 10M hits |</span><br><span class="line">+--------+------------+------------+------------+------------+------------+</span><br><span class="line">| 0 | 104 | 255 | 255 | 255 | 255 |</span><br><span class="line">+--------+------------+------------+------------+------------+------------+</span><br><span class="line">| 1 | 18 | 49 | 255 | 255 | 255 |</span><br><span class="line">+--------+------------+------------+------------+------------+------------+</span><br><span class="line">| 10 | 10 | 18 | 142 | 255 | 255 |</span><br><span class="line">+--------+------------+------------+------------+------------+------------+</span><br><span class="line">| 100 | 8 | 11 | 49 | 143 | 255 |</span><br><span class="line">+--------+------------+------------+------------+------------+------------+</span><br></pre></td></tr></table></figure>
|
|
<p>简而言之就是 lfu_log_factor 越大变化的越慢</p>
|
|
<h3 id="总结"><a href="#总结" class="headerlink" title="总结"></a>总结</h3><p>总结一下，redis 实现了近似的 lru 淘汰策略，通过增加了淘汰 key 的池子(pool)，并且增大每次抽样的 key 的数量来将淘汰效果更进一步地接近于 lru，这是 lru 策略，但是对于前面举的一个例子，其实 lru 并不能保证 key 的淘汰就如我们预期，所以在后期又引入了 lfu 的策略，lfu的策略比较巧妙，复用了 redis 对象的 lru 字段，并且使用了factor 参数来控制计数器递增的速度，防止 8 位的计数器太早溢出。</p>
|
|
|
|
</div>
|
|
|
|
|
|
|
|
|
|
|
|
<div class="popular-posts-header">Related Posts</div>
|
|
<ul class="popular-posts">
|
|
<li class="popular-posts-item">
|
|
<div class="popular-posts-title"><a href="/2020/01/10/redis数据结构介绍三/" rel="bookmark">redis数据结构介绍三-第三部分 整数集合</a></div>
|
|
</li>
|
|
<li class="popular-posts-item">
|
|
<div class="popular-posts-title"><a href="/2020/01/04/redis数据结构介绍二/" rel="bookmark">redis数据结构介绍二-第二部分 跳表</a></div>
|
|
</li>
|
|
<li class="popular-posts-item">
|
|
<div class="popular-posts-title"><a href="/2020/01/20/redis数据结构介绍五/" rel="bookmark">redis数据结构介绍五-第五部分 对象</a></div>
|
|
</li>
|
|
<li class="popular-posts-item">
|
|
<div class="popular-posts-title"><a href="/2020/01/19/redis数据结构介绍四/" rel="bookmark">redis数据结构介绍四-第四部分 压缩表</a></div>
|
|
</li>
|
|
<li class="popular-posts-item">
|
|
<div class="popular-posts-title"><a href="/2019/12/26/redis数据结构介绍/" rel="bookmark">redis数据结构介绍-第一部分 SDS，链表，字典</a></div>
|
|
</li>
|
|
</ul>
|
|
|
|
<div class="reward-container">
|
|
<div>请我喝杯咖啡</div>
|
|
<button onclick="var qr = document.getElementById('qr'); qr.style.display = (qr.style.display === 'none') ? 'block' : 'none';">
|
|
Donate
|
|
</button>
|
|
<div id="qr" style="display: none;">
|
|
|
|
<div style="display: inline-block;">
|
|
<img src="https://i.loli.net/2020/01/12/NUlWanT31E8LQGx.png" alt="Nicksxs WeChat Pay">
|
|
<p>WeChat Pay</p>
|
|
</div>
|
|
|
|
<div style="display: inline-block;">
|
|
<img src="https://ooo.0o0.ooo/2016/08/17/57b421e773057.jpg" alt="Nicksxs Alipay">
|
|
<p>Alipay</p>
|
|
</div>
|
|
|
|
</div>
|
|
</div>
|
|
|
|
|
|
|
|
<div>
|
|
<ul class="post-copyright">
|
|
<li class="post-copyright-author">
|
|
<strong>Post author: </strong>Nicksxs
|
|
</li>
|
|
<li class="post-copyright-link">
|
|
<strong>Post link: </strong>
|
|
<a href="https://nicksxs.me/2020/04/18/redis%E7%B3%BB%E5%88%97%E4%BB%8B%E7%BB%8D%E5%85%AB/" title="redis系列介绍八-淘汰策略">https://nicksxs.me/2020/04/18/redis系列介绍八/</a>
|
|
</li>
|
|
<li class="post-copyright-license">
|
|
<strong>Copyright Notice: </strong>All articles in this blog are licensed under <a href="https://creativecommons.org/licenses/by-nc-sa/4.0/" rel="noopener" target="_blank"><i class="fab fa-fw fa-creative-commons"></i>BY-NC-SA</a> unless stating additionally.
|
|
</li>
|
|
</ul>
|
|
</div>
|
|
|
|
|
|
<footer class="post-footer">
|
|
<div class="post-tags">
|
|
<a href="/tags/redis/" rel="tag"># redis</a>
|
|
<a href="/tags/%E6%95%B0%E6%8D%AE%E7%BB%93%E6%9E%84/" rel="tag"># 数据结构</a>
|
|
<a href="/tags/%E6%BA%90%E7%A0%81/" rel="tag"># 源码</a>
|
|
</div>
|
|
|
|
|
|
|
|
|
|
|
|
<div class="post-nav">
|
|
<div class="post-nav-item">
|
|
<a href="/2020/04/12/redis%E7%B3%BB%E5%88%97%E4%BB%8B%E7%BB%8D%E4%B8%83/" rel="prev" title="redis系列介绍七-过期策略">
|
|
<i class="fa fa-chevron-left"></i> redis系列介绍七-过期策略
|
|
</a></div>
|
|
<div class="post-nav-item">
|
|
<a href="/2020/04/26/%E8%81%8A%E8%81%8A-mysql-%E7%9A%84-MVCC/" rel="next" title="聊聊 mysql 的 MVCC">
|
|
聊聊 mysql 的 MVCC <i class="fa fa-chevron-right"></i>
|
|
</a></div>
|
|
</div>
|
|
</footer>
|
|
|
|
</article>
|
|
|
|
|
|
|
|
|
|
|
|
|
|
</div>
|
|
|
|
|
|
<div class="comments">
|
|
<div id="disqus_thread">
|
|
<noscript>Please enable JavaScript to view the comments powered by Disqus.</noscript>
|
|
</div>
|
|
</div>
|
|
|
|
|
|
<script>
|
|
window.addEventListener('tabs:register', () => {
|
|
let { activeClass } = CONFIG.comments;
|
|
if (CONFIG.comments.storage) {
|
|
activeClass = localStorage.getItem('comments_active') || activeClass;
|
|
}
|
|
if (activeClass) {
|
|
let activeTab = document.querySelector(`a[href="#comment-${activeClass}"]`);
|
|
if (activeTab) {
|
|
activeTab.click();
|
|
}
|
|
}
|
|
});
|
|
if (CONFIG.comments.storage) {
|
|
window.addEventListener('tabs:click', event => {
|
|
if (!event.target.matches('.tabs-comment .tab-content .tab-pane')) return;
|
|
let commentClass = event.target.classList[1];
|
|
localStorage.setItem('comments_active', commentClass);
|
|
});
|
|
}
|
|
</script>
|
|
|
|
</div>
|
|
|
|
|
|
<div class="toggle sidebar-toggle">
|
|
<span class="toggle-line toggle-line-first"></span>
|
|
<span class="toggle-line toggle-line-middle"></span>
|
|
<span class="toggle-line toggle-line-last"></span>
|
|
</div>
|
|
|
|
<aside class="sidebar">
|
|
<div class="sidebar-inner">
|
|
|
|
<ul class="sidebar-nav motion-element">
|
|
<li class="sidebar-nav-toc">
|
|
Table of Contents
|
|
</li>
|
|
<li class="sidebar-nav-overview">
|
|
Overview
|
|
</li>
|
|
</ul>
|
|
|
|
<!--noindex-->
|
|
<div class="post-toc-wrap sidebar-panel">
|
|
<div class="post-toc motion-element"><ol class="nav"><li class="nav-item nav-level-3"><a class="nav-link" href="#LRU"><span class="nav-number">1.</span> <span class="nav-text">LRU</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#LFU"><span class="nav-number">2.</span> <span class="nav-text">LFU</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#总结"><span class="nav-number">3.</span> <span class="nav-text">总结</span></a></li></ol></div>
|
|
</div>
|
|
<!--/noindex-->
|
|
|
|
<div class="site-overview-wrap sidebar-panel">
|
|
<div class="site-author motion-element" itemprop="author" itemscope itemtype="http://schema.org/Person">
|
|
<img class="site-author-image" itemprop="image" alt="Nicksxs"
|
|
src="/uploads/avatar.jpg">
|
|
<p class="site-author-name" itemprop="name">Nicksxs</p>
|
|
<div class="site-description" itemprop="description">learn from zero,技术博客，Nicksxs，史学森</div>
|
|
</div>
|
|
<div class="site-state-wrap motion-element">
|
|
<nav class="site-state">
|
|
<div class="site-state-item site-state-posts">
|
|
<a href="/archives/">
|
|
|
|
<span class="site-state-item-count">65</span>
|
|
<span class="site-state-item-name">posts</span>
|
|
</a>
|
|
</div>
|
|
<div class="site-state-item site-state-categories">
|
|
<a href="/categories/">
|
|
|
|
<span class="site-state-item-count">73</span>
|
|
<span class="site-state-item-name">categories</span></a>
|
|
</div>
|
|
<div class="site-state-item site-state-tags">
|
|
<a href="/tags/">
|
|
|
|
<span class="site-state-item-count">106</span>
|
|
<span class="site-state-item-name">tags</span></a>
|
|
</div>
|
|
</nav>
|
|
</div>
|
|
<div class="links-of-author motion-element">
|
|
<span class="links-of-author-item">
|
|
<a href="https://github.com/nicksxs" title="GitHub → https://github.com/nicksxs" rel="noopener" target="_blank"><i class="github fa-fw"></i>GitHub</a>
|
|
</span>
|
|
<span class="links-of-author-item">
|
|
<a href="mailto:nicksxs1202@gmail.com" title="E-Mail → mailto:nicksxs1202@gmail.com" rel="noopener" target="_blank"><i class="envelope fa-fw"></i>E-Mail</a>
|
|
</span>
|
|
<span class="links-of-author-item">
|
|
<a href="/atom.xml" title="RSS → /atom.xml"><i class="rss fa-fw"></i>RSS</a>
|
|
</span>
|
|
</div>
|
|
<div class="cc-license motion-element" itemprop="license">
|
|
<a href="https://creativecommons.org/licenses/by-nc-sa/4.0/" class="cc-opacity" rel="noopener" target="_blank"><img src="/images/cc-by-nc-sa.svg" alt="Creative Commons"></a>
|
|
</div>
|
|
|
|
<script type="text/javascript" charset="utf-8" src="/js/tagcloud.js"></script>
|
|
<script type="text/javascript" charset="utf-8" src="/js/tagcanvas.js"></script>
|
|
<div class="widget-wrap">
|
|
<div id="myCanvasContainer" class="widget tagcloud">
|
|
<canvas width="250" height="250" id="resCanvas" style="width=100%">
|
|
<ul class="tag-list" itemprop="keywords"><li class="tag-list-item"><a class="tag-list-link" href="/tags/2019/" rel="tag">2019</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/2020/" rel="tag">2020</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/2PC/" rel="tag">2PC</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/3PC/" rel="tag">3PC</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/AOP/" rel="tag">AOP</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/Adaptive/" rel="tag">Adaptive</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/Broker/" rel="tag">Broker</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/C/" rel="tag">C</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/C/" rel="tag">C++</a><span class="tag-list-count">3</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/Comparator/" rel="tag">Comparator</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/DefaultMQPushConsumer/" rel="tag">DefaultMQPushConsumer</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/Design-Patterns/" rel="tag">Design Patterns</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/Distributed-Lock/" rel="tag">Distributed Lock</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/Docker/" rel="tag">Docker</a><span class="tag-list-count">4</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/Dockerfile/" rel="tag">Dockerfile</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/Dubbo/" rel="tag">Dubbo</a><span class="tag-list-count">2</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/Filter/" rel="tag">Filter</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/G1/" rel="tag">G1</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/GC/" rel="tag">GC</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/Garbage-First-Collector/" rel="tag">Garbage-First Collector</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/Gogs/" rel="tag">Gogs</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/Homebrew/" rel="tag">Homebrew</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/Interceptor/" rel="tag">Interceptor</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/JMap/" rel="tag">JMap</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/JPS/" rel="tag">JPS</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/JStack/" rel="tag">JStack</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/JVM/" rel="tag">JVM</a><span class="tag-list-count">2</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/Java/" rel="tag">Java</a><span class="tag-list-count">9</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/MQ/" rel="tag">MQ</a><span class="tag-list-count">4</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/Mac/" rel="tag">Mac</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/Maven/" rel="tag">Maven</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/NameServer/" rel="tag">NameServer</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/PHP/" rel="tag">PHP</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/RPC/" rel="tag">RPC</a><span class="tag-list-count">2</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/Redis/" rel="tag">Redis</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/RocketMQ/" rel="tag">RocketMQ</a><span class="tag-list-count">4</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/SPI/" rel="tag">SPI</a><span class="tag-list-count">2</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/Servlet/" rel="tag">Servlet</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/Singleton/" rel="tag">Singleton</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/Spring/" rel="tag">Spring</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/Stream/" rel="tag">Stream</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/Thread-dump/" rel="tag">Thread dump</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/Tomcat/" rel="tag">Tomcat</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/Web/" rel="tag">Web</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/Webhook/" rel="tag">Webhook</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/aqs/" rel="tag">aqs</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/c/" rel="tag">c++</a><span class="tag-list-count">14</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/cgroup/" rel="tag">cgroup</a><span class="tag-list-count">2</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/cluster/" rel="tag">cluster</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/docker/" rel="tag">docker</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/echo/" rel="tag">echo</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/gap-lock/" rel="tag">gap lock</a><span class="tag-list-count">2</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/grep/" rel="tag">grep</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/hadoop/" rel="tag">hadoop</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/icu4c/" rel="tag">icu4c</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/im/" rel="tag">im</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/java/" rel="tag">java</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/leetcode/" rel="tag">leetcode</a><span class="tag-list-count">13</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/linux/" rel="tag">linux</a><span class="tag-list-count">2</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/mfc/" rel="tag">mfc</a><span class="tag-list-count">2</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/mq/" rel="tag">mq</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/mvcc/" rel="tag">mvcc</a><span class="tag-list-count">3</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/mysql/" rel="tag">mysql</a><span class="tag-list-count">4</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/namespace/" rel="tag">namespace</a><span class="tag-list-count">3</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/next-key-lock/" rel="tag">next-key lock</a><span class="tag-list-count">2</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/nginx/" rel="tag">nginx</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/nullsfirst/" rel="tag">nullsfirst</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/openresty/" rel="tag">openresty</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/php/" rel="tag">php</a><span class="tag-list-count">2</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/python/" rel="tag">python</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/read-view/" rel="tag">read view</a><span class="tag-list-count">3</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/redis/" rel="tag">redis</a><span class="tag-list-count">8</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/sort/" rel="tag">sort</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/spark/" rel="tag">spark</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/swoole/" rel="tag">swoole</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/uname/" rel="tag">uname</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/websocket/" rel="tag">websocket</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/zsh/" rel="tag">zsh</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E4%B8%89%E9%98%B6%E6%AE%B5%E6%8F%90%E4%BA%A4/" rel="tag">三阶段提交</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E4%B8%A4%E9%98%B6%E6%AE%B5%E6%8F%90%E4%BA%A4/" rel="tag">两阶段提交</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E4%B8%AD%E9%97%B4%E4%BB%B6/" rel="tag">中间件</a><span class="tag-list-count">4</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E5%87%8F%E8%82%A5/" rel="tag">减肥</a><span class="tag-list-count">3</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E5%88%86%E5%B8%83%E5%BC%8F%E4%BA%8B%E5%8A%A1/" rel="tag">分布式事务</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E5%88%86%E5%B8%83%E5%BC%8F%E9%94%81/" rel="tag">分布式锁</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E5%89%8A%E5%B3%B0%E5%A1%AB%E8%B0%B7/" rel="tag">削峰填谷</a><span class="tag-list-count">4</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E5%8D%95%E4%BE%8B/" rel="tag">单例</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E5%8D%9A%E5%AE%A2%EF%BC%8C%E6%96%87%E7%AB%A0/" rel="tag">博客，文章</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E5%8F%91%E8%A1%8C%E7%89%88/" rel="tag">发行版</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E5%AF%84%E7%94%9F%E8%99%AB/" rel="tag">寄生虫</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E5%B9%B2%E6%B4%BB/" rel="tag">干活</a><span class="tag-list-count">2</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E5%B9%B4%E4%B8%AD%E6%80%BB%E7%BB%93/" rel="tag">年中总结</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E5%B9%B4%E7%BB%88%E6%80%BB%E7%BB%93/" rel="tag">年终总结</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E5%B9%BB%E8%AF%BB/" rel="tag">幻读</a><span class="tag-list-count">2</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E5%BD%B1%E8%AF%84/" rel="tag">影评</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E6%8E%92%E5%BA%8F/" rel="tag">排序</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E6%95%B0%E6%8D%AE%E7%BB%93%E6%9E%84/" rel="tag">数据结构</a><span class="tag-list-count">11</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E6%B6%88%E6%81%AF%E9%98%9F%E5%88%97/" rel="tag">消息队列</a><span class="tag-list-count">4</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E6%BA%90%E7%A0%81/" rel="tag">源码</a><span class="tag-list-count">11</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E6%BA%90%E7%A0%81%E8%A7%A3%E6%9E%90/" rel="tag">源码解析</a><span class="tag-list-count">3</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E7%94%9F%E6%B4%BB/" rel="tag">生活</a><span class="tag-list-count">6</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E8%87%AA%E9%80%82%E5%BA%94%E6%8B%93%E5%B1%95/" rel="tag">自适应拓展</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E8%AE%BE%E8%AE%A1%E6%A8%A1%E5%BC%8F/" rel="tag">设计模式</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E8%AF%BB%E5%90%8E%E6%84%9F/" rel="tag">读后感</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E8%B7%91%E6%AD%A5/" rel="tag">跑步</a><span class="tag-list-count">3</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E8%BD%AC%E4%B9%89/" rel="tag">转义</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E8%BF%90%E5%8A%A8/" rel="tag">运动</a><span class="tag-list-count">3</span></li></ul>
|
|
</canvas>
|
|
</div>
|
|
</div>
|
|
|
|
|
|
|
|
<div class="links-of-blogroll motion-element">
|
|
<div class="links-of-blogroll-title"><i class="fa fa-link fa-fw"></i>
|
|
Links
|
|
</div>
|
|
<ul class="links-of-blogroll-list">
|
|
<li class="links-of-blogroll-item">
|
|
<a href="https://covermusic.cn/" title="https://covermusic.cn" rel="noopener" target="_blank">69伙伴</a>
|
|
</li>
|
|
</ul>
|
|
</div>
|
|
|
|
</div>
|
|
|
|
</div>
|
|
</aside>
|
|
<div id="sidebar-dimmer"></div>
|
|
|
|
|
|
</div>
|
|
</main>
|
|
|
|
<footer class="footer">
|
|
<div class="footer-inner">
|
|
|
|
|
|
|
|
|
|
<div class="copyright">
|
|
|
|
©
|
|
<span itemprop="copyrightYear">2020</span>
|
|
<span class="with-love">
|
|
<i class="fa fa-heart"></i>
|
|
</span>
|
|
<span class="author" itemprop="copyrightHolder">Nicksxs</span>
|
|
</div>
|
|
<div class="powered-by">Powered by <a href="https://hexo.io/" class="theme-link" rel="noopener" target="_blank">Hexo</a> & <a href="https://pisces.theme-next.org/" class="theme-link" rel="noopener" target="_blank">NexT.Pisces</a>
|
|
</div>
|
|
|
|
|
|
<div class="busuanzi-count">
|
|
<script async src="https://busuanzi.ibruce.info/busuanzi/2.3/busuanzi.pure.mini.js"></script>
|
|
<span class="post-meta-item" id="busuanzi_container_site_uv" style="display: none;">
|
|
<span class="post-meta-item-icon">
|
|
<i class="fa fa-user"></i>
|
|
</span>
|
|
<span class="site-uv" title="Total Visitors">
|
|
<span id="busuanzi_value_site_uv"></span>
|
|
</span>
|
|
</span>
|
|
<span class="post-meta-divider">|</span>
|
|
<span class="post-meta-item" id="busuanzi_container_site_pv" style="display: none;">
|
|
<span class="post-meta-item-icon">
|
|
<i class="fa fa-eye"></i>
|
|
</span>
|
|
<span class="site-pv" title="Total Views">
|
|
<span id="busuanzi_value_site_pv"></span>
|
|
</span>
|
|
</span>
|
|
</div>
|
|
|
|
|
|
|
|
|
|
|
|
|
|
<script>
|
|
(function() {
|
|
function leancloudSelector(url) {
|
|
url = encodeURI(url);
|
|
return document.getElementById(url).querySelector('.leancloud-visitors-count');
|
|
}
|
|
|
|
function addCount(Counter) {
|
|
var visitors = document.querySelector('.leancloud_visitors');
|
|
var url = decodeURI(visitors.id);
|
|
var title = visitors.dataset.flagTitle;
|
|
|
|
Counter('get', '/classes/Counter?where=' + encodeURIComponent(JSON.stringify({ url })))
|
|
.then(response => response.json())
|
|
.then(({ results }) => {
|
|
if (results.length > 0) {
|
|
var counter = results[0];
|
|
leancloudSelector(url).innerText = counter.time + 1;
|
|
Counter('put', '/classes/Counter/' + counter.objectId, { time: { '__op': 'Increment', 'amount': 1 } })
|
|
.catch(error => {
|
|
console.error('Failed to save visitor count', error);
|
|
});
|
|
} else {
|
|
leancloudSelector(url).innerText = 'Counter not initialized! More info at console err msg.';
|
|
console.error('ATTENTION! LeanCloud counter has security bug, see how to solve it here: https://github.com/theme-next/hexo-leancloud-counter-security. \n However, you can still use LeanCloud without security, by setting `security` option to `false`.');
|
|
|
|
}
|
|
})
|
|
.catch(error => {
|
|
console.error('LeanCloud Counter Error', error);
|
|
});
|
|
}
|
|
|
|
function showTime(Counter) {
|
|
var visitors = document.querySelectorAll('.leancloud_visitors');
|
|
var entries = [...visitors].map(element => {
|
|
return decodeURI(element.id);
|
|
});
|
|
|
|
Counter('get', '/classes/Counter?where=' + encodeURIComponent(JSON.stringify({ url: { '$in': entries } })))
|
|
.then(response => response.json())
|
|
.then(({ results }) => {
|
|
for (let url of entries) {
|
|
let target = results.find(item => item.url === url);
|
|
leancloudSelector(url).innerText = target ? target.time : 0;
|
|
}
|
|
})
|
|
.catch(error => {
|
|
console.error('LeanCloud Counter Error', error);
|
|
});
|
|
}
|
|
|
|
let { app_id, app_key, server_url } = {"enable":true,"app_id":"ysza182Vghlqjdt7QiwGLLJy-gzGzoHsz","app_key":"s9GDqbn7gnGGkusf66YRVccw","server_url":"https://leancloud.cn","security":true};
|
|
function fetchData(api_server) {
|
|
var Counter = (method, url, data) => {
|
|
return fetch(`${api_server}/1.1${url}`, {
|
|
method,
|
|
headers: {
|
|
'X-LC-Id' : app_id,
|
|
'X-LC-Key' : app_key,
|
|
'Content-Type': 'application/json',
|
|
},
|
|
body: JSON.stringify(data)
|
|
});
|
|
};
|
|
if (CONFIG.page.isPost) {
|
|
if (CONFIG.hostname !== location.hostname) return;
|
|
addCount(Counter);
|
|
} else if (document.querySelectorAll('.post-title-link').length >= 1) {
|
|
showTime(Counter);
|
|
}
|
|
}
|
|
|
|
let api_server = app_id.slice(-9) !== '-MdYXbMMI' ? server_url : `https://${app_id.slice(0, 8).toLowerCase()}.api.lncldglobal.com`;
|
|
|
|
if (api_server) {
|
|
fetchData(api_server);
|
|
} else {
|
|
fetch('https://app-router.leancloud.cn/2/route?appId=' + app_id)
|
|
.then(response => response.json())
|
|
.then(({ api_server }) => {
|
|
fetchData('https://' + api_server);
|
|
});
|
|
}
|
|
})();
|
|
</script>
|
|
|
|
|
|
</div>
|
|
</footer>
|
|
</div>
|
|
|
|
|
|
<script src="/lib/anime.min.js"></script>
|
|
<script src="//cdn.jsdelivr.net/npm/jquery@3/dist/jquery.min.js"></script>
|
|
<script src="//cdn.jsdelivr.net/gh/fancyapps/fancybox@3/dist/jquery.fancybox.min.js"></script>
|
|
<script src="//cdn.jsdelivr.net/npm/lozad@1/dist/lozad.min.js"></script>
|
|
<script src="/lib/velocity/velocity.min.js"></script>
|
|
<script src="/lib/velocity/velocity.ui.min.js"></script>
|
|
|
|
<script src="/js/utils.js"></script>
|
|
|
|
<script src="/js/motion.js"></script>
|
|
|
|
|
|
<script src="/js/schemes/pisces.js"></script>
|
|
|
|
|
|
<script src="/js/next-boot.js"></script>
|
|
|
|
|
|
|
|
|
|
|
|
<script>
|
|
(function(){
|
|
var bp = document.createElement('script');
|
|
var curProtocol = window.location.protocol.split(':')[0];
|
|
bp.src = (curProtocol === 'https') ? 'https://zz.bdstatic.com/linksubmit/push.js' : 'http://push.zhanzhang.baidu.com/push.js';
|
|
var s = document.getElementsByTagName("script")[0];
|
|
s.parentNode.insertBefore(bp, s);
|
|
})();
|
|
</script>
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
<script src="//cdn.jsdelivr.net/npm/quicklink@1/dist/quicklink.umd.js"></script>
|
|
<script>
|
|
window.addEventListener('load', () => {
|
|
quicklink({
|
|
timeout : 3000,
|
|
priority: true,
|
|
ignores : [uri => uri.includes('#'),uri => uri === 'https://nicksxs.me/2020/04/18/redis%E7%B3%BB%E5%88%97%E4%BB%8B%E7%BB%8D%E5%85%AB/',]
|
|
});
|
|
});
|
|
</script>
|
|
|
|
<script>
|
|
function loadCount() {
|
|
var d = document, s = d.createElement('script');
|
|
s.src = 'https://nicksxs.disqus.com/count.js';
|
|
s.id = 'dsq-count-scr';
|
|
(d.head || d.body).appendChild(s);
|
|
}
|
|
// defer loading until the whole page loading is completed
|
|
window.addEventListener('load', loadCount, false);
|
|
</script>
|
|
<script>
|
|
var disqus_config = function() {
|
|
this.page.url = "https://nicksxs.me/2020/04/18/redis%E7%B3%BB%E5%88%97%E4%BB%8B%E7%BB%8D%E5%85%AB/";
|
|
this.page.identifier = "2020/04/18/redis系列介绍八/";
|
|
this.page.title = "redis系列介绍八-淘汰策略";
|
|
};
|
|
NexT.utils.loadComments(document.querySelector('#disqus_thread'), () => {
|
|
if (window.DISQUS) {
|
|
DISQUS.reset({
|
|
reload: true,
|
|
config: disqus_config
|
|
});
|
|
} else {
|
|
var d = document, s = d.createElement('script');
|
|
s.src = 'https://nicksxs.disqus.com/embed.js';
|
|
s.setAttribute('data-timestamp', '' + +new Date());
|
|
(d.head || d.body).appendChild(s);
|
|
}
|
|
});
|
|
</script>
|
|
|
|
</body>
|
|
</html>
|