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content="redis"><meta property="article:tag" content="数据结构"><meta property="article:tag" content="源码"><meta name="twitter:card" content="summary"><link rel="canonical" href="https://nicksxs.me/2020/04/12/redis%E7%B3%BB%E5%88%97%E4%BB%8B%E7%BB%8D%E4%B8%83/"><script class="next-config" data-name="page" type="application/json">{"sidebar":"","isHome":false,"isPost":true,"lang":"zh-Hans","comments":true,"permalink":"https://nicksxs.me/2020/04/12/redis%E7%B3%BB%E5%88%97%E4%BB%8B%E7%BB%8D%E4%B8%83/","path":"2020/04/12/redis系列介绍七/","title":"redis系列介绍七-过期策略"}</script><script class="next-config" data-name="calendar" type="application/json">""</script><title>redis系列介绍七-过期策略 | Nicksxs's Blog</title><script async src="https://www.googletagmanager.com/gtag/js?id=UA-61358619-1"></script><script class="next-config" data-name="google_analytics" type="application/json">{"tracking_id":"UA-61358619-1","only_pageview":false}</script><script 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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/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/is-not-null/" rel="tag">is not null</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/is-null/" rel="tag">is null</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/j-u-c/" rel="tag">j.u.c</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">16</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/jvm/" rel="tag">jvm</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">25</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/leetcode-155/" rel="tag">leetcode 155</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/linked-list/" rel="tag">linked list</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/linux/" rel="tag">linux</a><span class="tag-list-count">3</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/lock/" rel="tag">lock</a><span class="tag-list-count">1</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/min-stack/" rel="tag">min stack</a><span class="tag-list-count">1</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">5</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/procedure/" rel="tag">procedure</a><span class="tag-list-count">1</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">11</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/signal/" rel="tag">signal</a><span class="tag-list-count">1</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/stack/" rel="tag">stack</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/string/" rel="tag">string</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/top/" rel="tag">top</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/unlock/" rel="tag">unlock</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/value/" rel="tag">value</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%8D%E5%8F%AF%E5%8F%98%E5%BC%95%E7%94%A8/" rel="tag">不可变引用</a><span class="tag-list-count">2</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E4%B8%9C%E4%BA%AC%E5%A5%A5%E8%BF%90%E4%BC%9A/" rel="tag">东京奥运会</a><span class="tag-list-count">2</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%E5%B1%B1%E8%B7%AF/" rel="tag">中山路</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E4%B8%AD%E5%BA%8F/" rel="tag">中序</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/%E4%B8%BE%E9%87%8D/" rel="tag">举重</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E4%B9%92%E4%B9%93%E7%90%83/" rel="tag">乒乓球</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E4%BA%8C%E5%8F%89%E6%A0%91/" rel="tag">二叉树</a><span class="tag-list-count">3</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E4%BA%92%E6%96%A5%E9%94%81/" rel="tag">互斥锁</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E4%BB%A3%E7%A0%81%E9%A2%98%E8%A7%A3/" rel="tag">代码题解</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E4%BF%AE%E7%94%B5%E8%84%91%E7%9A%84/" rel="tag">修电脑的</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E5%81%8F%E5%90%91%E9%94%81/" rel="tag">偏向锁</a><span class="tag-list-count">2</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E5%81%A5%E5%BA%B7%E7%A0%81/" rel="tag">健康码</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E5%85%AC%E4%BA%A4/" rel="tag">公交</a><span class="tag-list-count">2</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E5%85%AC%E4%BA%A4%E8%BD%A6/" rel="tag">公交车</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E5%86%85%E5%AD%98%E5%88%86%E5%B8%83/" rel="tag">内存分布</a><span class="tag-list-count">3</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E5%86%85%E5%AD%98%E6%B3%84%E6%BC%8F/" rel="tag">内存泄漏</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E5%87%86%E5%A4%87/" rel="tag">准备</a><span class="tag-list-count">1</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">6</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%88%87%E7%89%87/" rel="tag">切片</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E5%88%9D%E5%A7%8B%E5%8C%96/" rel="tag">初始化</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%89%8D%E5%BA%8F/" rel="tag">前序</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E5%8A%A0%E5%A1%9E/" rel="tag">加塞</a><span class="tag-list-count">3</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E5%8A%A0%E8%BD%BD/" rel="tag">加载</a><span class="tag-list-count">1</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%8E%A6%E9%97%A8/" rel="tag">厦门</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E5%8F%8C%E4%BA%B2%E5%A7%94%E6%B4%BE/" rel="tag">双亲委派</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%8F%A3%E7%BD%A9/" rel="tag">口罩</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E5%8F%AF%E5%8F%98%E5%BC%95%E7%94%A8/" rel="tag">可变引用</a><span class="tag-list-count">2</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E5%90%90%E6%A7%BD/" rel="tag">吐槽</a><span class="tag-list-count">2</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E5%9E%83%E5%9C%BE%E5%9B%9E%E6%94%B6/" rel="tag">垃圾回收</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E5%9F%BA%E7%A1%80%E8%AE%BE%E6%96%BD/" rel="tag">基础设施</a><span class="tag-list-count">2</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E5%AE%89%E5%85%A8/" rel="tag">安全</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E5%AE%B9%E9%94%99%E6%9C%BA%E5%88%B6/" rel="tag">容错机制</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%B0%84%E5%87%BB/" rel="tag">射击</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E5%B0%8F%E6%8A%80%E5%B7%A7/" rel="tag">小技巧</a><span class="tag-list-count">4</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E5%B1%80%E5%8F%A3%E8%A1%97/" rel="tag">局口街</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E5%B8%83%E9%9A%86%E8%BF%87%E6%BB%A4%E5%99%A8/" rel="tag">布隆过滤器</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">5</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">2</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">2</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E5%B9%B6%E5%8F%91/" rel="tag">并发</a><span class="tag-list-count">2</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E5%B9%B8%E7%A6%8F%E4%BA%86%E5%90%97/" rel="tag">幸福了吗</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%BA%94%E7%94%A8/" rel="tag">应用</a><span class="tag-list-count">2</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E5%BC%80%E8%BD%A6/" rel="tag">开车</a><span class="tag-list-count">3</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E5%BC%B1%E5%BC%95%E7%94%A8/" rel="tag">弱引用</a><span class="tag-list-count">1</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%89%80%E6%9C%89%E6%9D%83/" rel="tag">所有权</a><span class="tag-list-count">3</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E6%89%93%E5%8D%A1/" rel="tag">打卡</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E6%89%B6%E6%A2%AF/" rel="tag">扶梯</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E6%8A%80%E6%9C%AF/" rel="tag">技术</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E6%8B%96%E6%9B%B4/" rel="tag">拖更</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">2</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E6%8E%A5%E9%9B%A8%E6%B0%B4/" rel="tag">接雨水</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%96%B0%E8%AF%AD%E8%A8%80/" rel="tag">新语言</a><span class="tag-list-count">3</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E6%97%85%E6%B8%B8/" rel="tag">旅游</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E6%9B%BE%E5%8E%9D%E5%9E%B5/" rel="tag">曾厝垵</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E6%9C%80%E5%B0%8F%E6%A0%88/" rel="tag">最小栈</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E6%9D%80%E4%BA%BA%E8%AF%9B%E5%BF%83/" rel="tag">杀人诛心</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E6%9D%AD%E5%B7%9E/" rel="tag">杭州</a><span class="tag-list-count">3</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E6%A0%87%E8%AE%B0%E6%95%B4%E7%90%86/" rel="tag">标记整理</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E6%A4%8D%E7%89%A9%E5%9B%AD/" rel="tag">植物园</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E6%B2%99%E8%8C%B6%E9%9D%A2/" rel="tag">沙茶面</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a 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href="https://nicksxs.me/2020/04/12/redis%E7%B3%BB%E5%88%97%E4%BB%8B%E7%BB%8D%E4%B8%83/"><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系列介绍七-过期策略</h1><div class="post-meta-container"><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: 2020-04-12 21:22:00" itemprop="dateCreated datePublished" datetime="2020-04-12T21:22:00+08:00">2020-04-12</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="/2020/04/12/redis%E7%B3%BB%E5%88%97%E4%BB%8B%E7%BB%8D%E4%B8%83/" class="post-meta-item leancloud_visitors" data-flag-title="redis系列介绍七-过期策略" title="Views"><span class="post-meta-item-icon"><i class="far 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"><span class="post-meta-item-icon"><i class="far 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="/2020/04/12/redis%E7%B3%BB%E5%88%97%E4%BB%8B%E7%BB%8D%E4%B8%83/#disqus_thread" itemprop="discussionUrl"><span class="post-comments-count disqus-comment-count" data-disqus-identifier="2020/04/12/redis系列介绍七/" itemprop="commentCount"></span></a></span></div></div></header><div class="post-body" itemprop="articleBody"><p>这一篇不再是数据结构介绍了，大致的数据结构基本都介绍了，这一篇主要是查漏补缺，或者说讲一些重要且基本的概念，也可能是经常被忽略的，很多讲 redis 的系列文章可能都会忽略，学习 redis 的时候也会，因为觉得源码学习就是讲主要的数据结构和“算法”学习了就好了。<br>redis 的主要应用就是拿来作为高性能的缓存，那么缓存一般有些啥需要注意的，首先是访问速度，如果取得跟数据库一样快，那就没什么存在的意义，第二个是缓存的字面意思，我只是为了让数据读取快一些，通常大部分的场景这个是需要更新过期的，这里就把我要讲的第一点引出来了（真累，</p><h2 id="redis过期策略"><a href="#redis过期策略" class="headerlink" title="redis过期策略"></a>redis过期策略</h2><p>redis 是如何过期缓存的，可以猜测下，最无脑的就是每个设置了过期时间的 key 都设个定时器，过期了就删除，这种显然消耗太大，清理地最及时，还有的就是 redis 正在采用的懒汉清理策略和定期清理<br>懒汉策略就是在使用的时候去检查缓存是否过期，比如 get 操作时，先判断下这个 key 是否已经过期了，如果过期了就删掉，并且返回空，如果没过期则正常返回<br>主要代码是</p><pre class="line-numbers language-C" data-language="C"><code class="language-C">&#x2F;* This function is called when we are going to perform some operation
* in a given key, but such key may be already logically expired even if
* it still exists in the database. The main way this function is called
* is via lookupKey*() family of functions.
*
* The behavior of the function depends on the replication role of the
* instance, because slave instances do not expire keys, they wait
* for DELs from the master for consistency matters. However even
* slaves will try to have a coherent return value for the function,
* so that read commands executed in the slave side will be able to
* behave like if the key is expired even if still present (because the
* master has yet to propagate the DEL).
*
* In masters as a side effect of finding a key which is expired, such
* key will be evicted from the database. Also this may trigger the
* propagation of a DEL&#x2F;UNLINK command in AOF &#x2F; replication stream.
*
* The return value of the function is 0 if the key is still valid,
* otherwise the function returns 1 if the key is expired. *&#x2F;
int expireIfNeeded(redisDb *db, robj *key) &#123;
if (!keyIsExpired(db,key)) return 0;
&#x2F;* If we are running in the context of a slave, instead of
* evicting the expired key from the database, we return ASAP:
* the slave key expiration is controlled by the master that will
* send us synthesized DEL operations for expired keys.
*
* Still we try to return the right information to the caller,
* that is, 0 if we think the key should be still valid, 1 if
* we think the key is expired at this time. *&#x2F;
if (server.masterhost !&#x3D; NULL) return 1;
&#x2F;* Delete the key *&#x2F;
server.stat_expiredkeys++;
propagateExpire(db,key,server.lazyfree_lazy_expire);
notifyKeyspaceEvent(NOTIFY_EXPIRED,
&quot;expired&quot;,key,db-&gt;id);
return server.lazyfree_lazy_expire ? dbAsyncDelete(db,key) :
dbSyncDelete(db,key);
&#125;
&#x2F;* Check if the key is expired. *&#x2F;
int keyIsExpired(redisDb *db, robj *key) &#123;
mstime_t when &#x3D; getExpire(db,key);
mstime_t now;
if (when &lt; 0) return 0; &#x2F;* No expire for this key *&#x2F;
&#x2F;* Don&#39;t expire anything while loading. It will be done later. *&#x2F;
if (server.loading) return 0;
&#x2F;* If we are in the context of a Lua script, we pretend that time is
* blocked to when the Lua script started. This way a key can expire
* only the first time it is accessed and not in the middle of the
* script execution, making propagation to slaves &#x2F; AOF consistent.
* See issue #1525 on Github for more information. *&#x2F;
if (server.lua_caller) &#123;
now &#x3D; server.lua_time_start;
&#125;
&#x2F;* If we are in the middle of a command execution, we still want to use
* a reference time that does not change: in that case we just use the
* cached time, that we update before each call in the call() function.
* This way we avoid that commands such as RPOPLPUSH or similar, that
* may re-open the same key multiple times, can invalidate an already
* open object in a next call, if the next call will see the key expired,
* while the first did not. *&#x2F;
else if (server.fixed_time_expire &gt; 0) &#123;
now &#x3D; server.mstime;
&#125;
&#x2F;* For the other cases, we want to use the most fresh time we have. *&#x2F;
else &#123;
now &#x3D; mstime();
&#125;
&#x2F;* The key expired if the current (virtual or real) time is greater
* than the expire time of the key. *&#x2F;
return now &gt; when;
&#125;
&#x2F;* Return the expire time of the specified key, or -1 if no expire
* is associated with this key (i.e. the key is non volatile) *&#x2F;
long long getExpire(redisDb *db, robj *key) &#123;
dictEntry *de;
&#x2F;* No expire? return ASAP *&#x2F;
if (dictSize(db-&gt;expires) &#x3D;&#x3D; 0 ||
(de &#x3D; dictFind(db-&gt;expires,key-&gt;ptr)) &#x3D;&#x3D; NULL) return -1;
&#x2F;* The entry was found in the expire dict, this means it should also
* be present in the main dict (safety check). *&#x2F;
serverAssertWithInfo(NULL,key,dictFind(db-&gt;dict,key-&gt;ptr) !&#x3D; NULL);
return dictGetSignedIntegerVal(de);
&#125;<span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre><p>这里有几点要注意的，第一是当惰性删除时会根据lazyfree_lazy_expire这个参数去判断是执行同步删除还是异步删除，另外一点是对于 slave，是不需要执行的，因为会在 master 过期时向 slave 发送 del 指令。<br>光采用这个策略会有什么问题呢，假如一些key 一直未被访问，那这些 key 就不会过期了，导致一直被占用着内存，所以 redis 采取了懒汉式过期加定期过期策略，定期策略是怎么执行的呢</p><pre class="line-numbers language-C" data-language="C"><code class="language-C">&#x2F;* This function handles &#39;background&#39; operations we are required to do
* incrementally in Redis databases, such as active key expiring, resizing,
* rehashing. *&#x2F;
void databasesCron(void) &#123;
&#x2F;* Expire keys by random sampling. Not required for slaves
* as master will synthesize DELs for us. *&#x2F;
if (server.active_expire_enabled) &#123;
if (server.masterhost &#x3D;&#x3D; NULL) &#123;
activeExpireCycle(ACTIVE_EXPIRE_CYCLE_SLOW);
&#125; else &#123;
expireSlaveKeys();
&#125;
&#125;
&#x2F;* Defrag keys gradually. *&#x2F;
activeDefragCycle();
&#x2F;* Perform hash tables rehashing if needed, but only if there are no
* other processes saving the DB on disk. Otherwise rehashing is bad
* as will cause a lot of copy-on-write of memory pages. *&#x2F;
if (!hasActiveChildProcess()) &#123;
&#x2F;* We use global counters so if we stop the computation at a given
* DB we&#39;ll be able to start from the successive in the next
* cron loop iteration. *&#x2F;
static unsigned int resize_db &#x3D; 0;
static unsigned int rehash_db &#x3D; 0;
int dbs_per_call &#x3D; CRON_DBS_PER_CALL;
int j;
&#x2F;* Don&#39;t test more DBs than we have. *&#x2F;
if (dbs_per_call &gt; server.dbnum) dbs_per_call &#x3D; server.dbnum;
&#x2F;* Resize *&#x2F;
for (j &#x3D; 0; j &lt; dbs_per_call; j++) &#123;
tryResizeHashTables(resize_db % server.dbnum);
resize_db++;
&#125;
&#x2F;* Rehash *&#x2F;
if (server.activerehashing) &#123;
for (j &#x3D; 0; j &lt; dbs_per_call; j++) &#123;
int work_done &#x3D; incrementallyRehash(rehash_db);
if (work_done) &#123;
&#x2F;* If the function did some work, stop here, we&#39;ll do
* more at the next cron loop. *&#x2F;
break;
&#125; else &#123;
&#x2F;* If this db didn&#39;t need rehash, we&#39;ll try the next one. *&#x2F;
rehash_db++;
rehash_db %&#x3D; server.dbnum;
&#125;
&#125;
&#125;
&#125;
&#125;
&#x2F;* Try to expire a few timed out keys. The algorithm used is adaptive and
* will use few CPU cycles if there are few expiring keys, otherwise
* it will get more aggressive to avoid that too much memory is used by
* keys that can be removed from the keyspace.
*
* Every expire cycle tests multiple databases: the next call will start
* again from the next db, with the exception of exists for time limit: in that
* case we restart again from the last database we were processing. Anyway
* no more than CRON_DBS_PER_CALL databases are tested at every iteration.
*
* The function can perform more or less work, depending on the &quot;type&quot;
* argument. It can execute a &quot;fast cycle&quot; or a &quot;slow cycle&quot;. The slow
* cycle is the main way we collect expired cycles: this happens with
* the &quot;server.hz&quot; frequency (usually 10 hertz).
*
* However the slow cycle can exit for timeout, since it used too much time.
* For this reason the function is also invoked to perform a fast cycle
* at every event loop cycle, in the beforeSleep() function. The fast cycle
* will try to perform less work, but will do it much more often.
*
* The following are the details of the two expire cycles and their stop
* conditions:
*
* If type is ACTIVE_EXPIRE_CYCLE_FAST the function will try to run a
* &quot;fast&quot; expire cycle that takes no longer than EXPIRE_FAST_CYCLE_DURATION
* microseconds, and is not repeated again before the same amount of time.
* The cycle will also refuse to run at all if the latest slow cycle did not
* terminate because of a time limit condition.
*
* If type is ACTIVE_EXPIRE_CYCLE_SLOW, that normal expire cycle is
* executed, where the time limit is a percentage of the REDIS_HZ period
* as specified by the ACTIVE_EXPIRE_CYCLE_SLOW_TIME_PERC define. In the
* fast cycle, the check of every database is interrupted once the number
* of already expired keys in the database is estimated to be lower than
* a given percentage, in order to avoid doing too much work to gain too
* little memory.
*
* The configured expire &quot;effort&quot; will modify the baseline parameters in
* order to do more work in both the fast and slow expire cycles.
*&#x2F;
#define ACTIVE_EXPIRE_CYCLE_KEYS_PER_LOOP 20 &#x2F;* Keys for each DB loop. *&#x2F;
#define ACTIVE_EXPIRE_CYCLE_FAST_DURATION 1000 &#x2F;* Microseconds. *&#x2F;
#define ACTIVE_EXPIRE_CYCLE_SLOW_TIME_PERC 25 &#x2F;* Max % of CPU to use. *&#x2F;
#define ACTIVE_EXPIRE_CYCLE_ACCEPTABLE_STALE 10 &#x2F;* % of stale keys after which
we do extra efforts. *&#x2F;
void activeExpireCycle(int type) &#123;
&#x2F;* Adjust the running parameters according to the configured expire
* effort. The default effort is 1, and the maximum configurable effort
* is 10. *&#x2F;
unsigned long
effort &#x3D; server.active_expire_effort-1, &#x2F;* Rescale from 0 to 9. *&#x2F;
config_keys_per_loop &#x3D; ACTIVE_EXPIRE_CYCLE_KEYS_PER_LOOP +
ACTIVE_EXPIRE_CYCLE_KEYS_PER_LOOP&#x2F;4*effort,
config_cycle_fast_duration &#x3D; ACTIVE_EXPIRE_CYCLE_FAST_DURATION +
ACTIVE_EXPIRE_CYCLE_FAST_DURATION&#x2F;4*effort,
config_cycle_slow_time_perc &#x3D; ACTIVE_EXPIRE_CYCLE_SLOW_TIME_PERC +
2*effort,
config_cycle_acceptable_stale &#x3D; ACTIVE_EXPIRE_CYCLE_ACCEPTABLE_STALE-
effort;
&#x2F;* This function has some global state in order to continue the work
* incrementally across calls. *&#x2F;
static unsigned int current_db &#x3D; 0; &#x2F;* Last DB tested. *&#x2F;
static int timelimit_exit &#x3D; 0; &#x2F;* Time limit hit in previous call? *&#x2F;
static long long last_fast_cycle &#x3D; 0; &#x2F;* When last fast cycle ran. *&#x2F;
int j, iteration &#x3D; 0;
int dbs_per_call &#x3D; CRON_DBS_PER_CALL;
long long start &#x3D; ustime(), timelimit, elapsed;
&#x2F;* When clients are paused the dataset should be static not just from the
* POV of clients not being able to write, but also from the POV of
* expires and evictions of keys not being performed. *&#x2F;
if (clientsArePaused()) return;
if (type &#x3D;&#x3D; ACTIVE_EXPIRE_CYCLE_FAST) &#123;
&#x2F;* Don&#39;t start a fast cycle if the previous cycle did not exit
* for time limit, unless the percentage of estimated stale keys is
* too high. Also never repeat a fast cycle for the same period
* as the fast cycle total duration itself. *&#x2F;
if (!timelimit_exit &amp;&amp;
server.stat_expired_stale_perc &lt; config_cycle_acceptable_stale)
return;
if (start &lt; last_fast_cycle + (long long)config_cycle_fast_duration*2)
return;
last_fast_cycle &#x3D; start;
&#125;
&#x2F;* We usually should test CRON_DBS_PER_CALL per iteration, with
* two exceptions:
*
* 1) Don&#39;t test more DBs than we have.
* 2) If last time we hit the time limit, we want to scan all DBs
* in this iteration, as there is work to do in some DB and we don&#39;t want
* expired keys to use memory for too much time. *&#x2F;
if (dbs_per_call &gt; server.dbnum || timelimit_exit)
dbs_per_call &#x3D; server.dbnum;
&#x2F;* We can use at max &#39;config_cycle_slow_time_perc&#39; percentage of CPU
* time per iteration. Since this function gets called with a frequency of
* server.hz times per second, the following is the max amount of
* microseconds we can spend in this function. *&#x2F;
timelimit &#x3D; config_cycle_slow_time_perc*1000000&#x2F;server.hz&#x2F;100;
timelimit_exit &#x3D; 0;
if (timelimit &lt;&#x3D; 0) timelimit &#x3D; 1;
if (type &#x3D;&#x3D; ACTIVE_EXPIRE_CYCLE_FAST)
timelimit &#x3D; config_cycle_fast_duration; &#x2F;* in microseconds. *&#x2F;
&#x2F;* Accumulate some global stats as we expire keys, to have some idea
* about the number of keys that are already logically expired, but still
* existing inside the database. *&#x2F;
long total_sampled &#x3D; 0;
long total_expired &#x3D; 0;
for (j &#x3D; 0; j &lt; dbs_per_call &amp;&amp; timelimit_exit &#x3D;&#x3D; 0; j++) &#123;
&#x2F;* Expired and checked in a single loop. *&#x2F;
unsigned long expired, sampled;
redisDb *db &#x3D; server.db+(current_db % server.dbnum);
&#x2F;* Increment the DB now so we are sure if we run out of time
* in the current DB we&#39;ll restart from the next. This allows to
* distribute the time evenly across DBs. *&#x2F;
current_db++;
&#x2F;* Continue to expire if at the end of the cycle more than 25%
* of the keys were expired. *&#x2F;
do &#123;
unsigned long num, slots;
long long now, ttl_sum;
int ttl_samples;
iteration++;
&#x2F;* If there is nothing to expire try next DB ASAP. *&#x2F;
if ((num &#x3D; dictSize(db-&gt;expires)) &#x3D;&#x3D; 0) &#123;
db-&gt;avg_ttl &#x3D; 0;
break;
&#125;
slots &#x3D; dictSlots(db-&gt;expires);
now &#x3D; mstime();
&#x2F;* When there are less than 1% filled slots, sampling the key
* space is expensive, so stop here waiting for better times...
* The dictionary will be resized asap. *&#x2F;
if (num &amp;&amp; slots &gt; DICT_HT_INITIAL_SIZE &amp;&amp;
(num*100&#x2F;slots &lt; 1)) break;
&#x2F;* The main collection cycle. Sample random keys among keys
* with an expire set, checking for expired ones. *&#x2F;
expired &#x3D; 0;
sampled &#x3D; 0;
ttl_sum &#x3D; 0;
ttl_samples &#x3D; 0;
if (num &gt; config_keys_per_loop)
num &#x3D; config_keys_per_loop;
&#x2F;* Here we access the low level representation of the hash table
* for speed concerns: this makes this code coupled with dict.c,
* but it hardly changed in ten years.
*
* Note that certain places of the hash table may be empty,
* so we want also a stop condition about the number of
* buckets that we scanned. However scanning for free buckets
* is very fast: we are in the cache line scanning a sequential
* array of NULL pointers, so we can scan a lot more buckets
* than keys in the same time. *&#x2F;
long max_buckets &#x3D; num*20;
long checked_buckets &#x3D; 0;
while (sampled &lt; num &amp;&amp; checked_buckets &lt; max_buckets) &#123;
for (int table &#x3D; 0; table &lt; 2; table++) &#123;
if (table &#x3D;&#x3D; 1 &amp;&amp; !dictIsRehashing(db-&gt;expires)) break;
unsigned long idx &#x3D; db-&gt;expires_cursor;
idx &amp;&#x3D; db-&gt;expires-&gt;ht[table].sizemask;
dictEntry *de &#x3D; db-&gt;expires-&gt;ht[table].table[idx];
long long ttl;
&#x2F;* Scan the current bucket of the current table. *&#x2F;
checked_buckets++;
while(de) &#123;
&#x2F;* Get the next entry now since this entry may get
* deleted. *&#x2F;
dictEntry *e &#x3D; de;
de &#x3D; de-&gt;next;
ttl &#x3D; dictGetSignedIntegerVal(e)-now;
if (activeExpireCycleTryExpire(db,e,now)) expired++;
if (ttl &gt; 0) &#123;
&#x2F;* We want the average TTL of keys yet
* not expired. *&#x2F;
ttl_sum +&#x3D; ttl;
ttl_samples++;
&#125;
sampled++;
&#125;
&#125;
db-&gt;expires_cursor++;
&#125;
total_expired +&#x3D; expired;
total_sampled +&#x3D; sampled;
&#x2F;* Update the average TTL stats for this database. *&#x2F;
if (ttl_samples) &#123;
long long avg_ttl &#x3D; ttl_sum&#x2F;ttl_samples;
&#x2F;* Do a simple running average with a few samples.
* We just use the current estimate with a weight of 2%
* and the previous estimate with a weight of 98%. *&#x2F;
if (db-&gt;avg_ttl &#x3D;&#x3D; 0) db-&gt;avg_ttl &#x3D; avg_ttl;
db-&gt;avg_ttl &#x3D; (db-&gt;avg_ttl&#x2F;50)*49 + (avg_ttl&#x2F;50);
&#125;
&#x2F;* We can&#39;t block forever here even if there are many keys to
* expire. So after a given amount of milliseconds return to the
* caller waiting for the other active expire cycle. *&#x2F;
if ((iteration &amp; 0xf) &#x3D;&#x3D; 0) &#123; &#x2F;* check once every 16 iterations. *&#x2F;
elapsed &#x3D; ustime()-start;
if (elapsed &gt; timelimit) &#123;
timelimit_exit &#x3D; 1;
server.stat_expired_time_cap_reached_count++;
break;
&#125;
&#125;
&#x2F;* We don&#39;t repeat the cycle for the current database if there are
* an acceptable amount of stale keys (logically expired but yet
* not reclained). *&#x2F;
&#125; while ((expired*100&#x2F;sampled) &gt; config_cycle_acceptable_stale);
&#125;
elapsed &#x3D; ustime()-start;
server.stat_expire_cycle_time_used +&#x3D; elapsed;
latencyAddSampleIfNeeded(&quot;expire-cycle&quot;,elapsed&#x2F;1000);
&#x2F;* Update our estimate of keys existing but yet to be expired.
* Running average with this sample accounting for 5%. *&#x2F;
double current_perc;
if (total_sampled) &#123;
current_perc &#x3D; (double)total_expired&#x2F;total_sampled;
&#125; else
current_perc &#x3D; 0;
server.stat_expired_stale_perc &#x3D; (current_perc*0.05)+
(server.stat_expired_stale_perc*0.95);
&#125;<span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre><p>执行定期清除分成两种类型，快和慢，分别由<code>beforeSleep</code>和<code>databasesCron</code>调用，快版有两个限制，一个是执行时长由ACTIVE_EXPIRE_CYCLE_FAST_DURATION限制，另一个是执行间隔是 2 倍的ACTIVE_EXPIRE_CYCLE_FAST_DURATION，另外这还可以由配置的server.active_expire_effort参数来控制，默认是 1，最大是 10</p><pre class="line-numbers language-C" data-language="C"><code class="language-C">onfig_cycle_fast_duration &#x3D; ACTIVE_EXPIRE_CYCLE_FAST_DURATION +
ACTIVE_EXPIRE_CYCLE_FAST_DURATION&#x2F;4*effort<span aria-hidden="true" class="line-numbers-rows"><span></span><span></span></span></code></pre><p>然后会从一定数量的 db 中找出一定数量的带过期时间的 key（保存在 expires中），这里的数量是由</p><pre class="line-numbers language-C" data-language="C"><code class="language-C">config_keys_per_loop &#x3D; ACTIVE_EXPIRE_CYCLE_KEYS_PER_LOOP +
ACTIVE_EXPIRE_CYCLE_KEYS_PER_LOOP&#x2F;4*effort
&#96;&#96;&#96;
控制，慢速的执行时长是
&#96;&#96;&#96;C
config_cycle_slow_time_perc &#x3D; ACTIVE_EXPIRE_CYCLE_SLOW_TIME_PERC +
2*effort
timelimit &#x3D; config_cycle_slow_time_perc*1000000&#x2F;server.hz&#x2F;100;<span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre><p>这里还有一个额外的退出条件，如果当前数据库的抽样结果已经达到我们所允许的过期 key 百分比，则下次不再处理当前 db，继续处理下个 db</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="/2020/01/19/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="/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="/2020/01/22/redis数据结构介绍六/" rel="bookmark">redis数据结构介绍六 快表</a></div></li></ul><footer class="post-footer"><div class="reward-container"><div>Buy me a coffee</div><button>Donate</button><div class="post-reward"><div><img src="https://i.loli.net/2020/01/12/NUlWanT31E8LQGx.png" alt="Nicksxs WeChat Pay"> <span>WeChat Pay</span></div><div><img src="https://ooo.0o0.ooo/2016/08/17/57b421e773057.jpg" alt="Nicksxs Alipay"> <span>Alipay</span></div></div></div><div class="post-copyright"><ul><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/2020/04/12/redis%E7%B3%BB%E5%88%97%E4%BB%8B%E7%BB%8D%E4%B8%83/" title="redis系列介绍七-过期策略">https://nicksxs.me/2020/04/12/redis系列介绍七/</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><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="/2020/04/05/Comparator%E4%BD%BF%E7%94%A8%E5%B0%8F%E8%AE%B0/" rel="prev" title="Comparator使用小记"><i class="fa fa-chevron-left"></i> Comparator使用小记</a></div><div class="post-nav-item"><a href="/2020/04/18/redis%E7%B3%BB%E5%88%97%E4%BB%8B%E7%BB%8D%E5%85%AB/" rel="next" title="redis系列介绍八-淘汰策略">redis系列介绍八-淘汰策略 <i class="fa fa-chevron-right"></i></a></div></div></footer></article></div><div class="comments" id="disqus_thread"><noscript>Please enable JavaScript to view the comments powered by Disqus.</noscript></div></div></main><footer class="footer"><div class="footer-inner"><div class="copyright">&copy; 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