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159 KiB
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Theme: Default
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Description: Original highlight.js style
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License: see project LICENSE
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Touched: 2021
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href=/tags/Intersection-of-Two-Arrays/ rel=tag>Intersection of Two Arrays</a><span class=tag-list-count>1</span><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 class=tag-list-item><a class=tag-list-link href=/tags/JPS/ rel=tag>JPS</a><span class=tag-list-count>1</span><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 class=tag-list-item><a class=tag-list-link href=/tags/JVM/ rel=tag>JVM</a><span class=tag-list-count>2</span><li class=tag-list-item><a class=tag-list-link href=/tags/Java/ rel=tag>Java</a><span class=tag-list-count>75</span><li class=tag-list-item><a class=tag-list-link href=/tags/LLM/ rel=tag>LLM</a><span class=tag-list-count>2</span><li class=tag-list-item><a class=tag-list-link href=/tags/Leetcode-42/ rel=tag>Leetcode 42</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/LimitedThreadPool/ rel=tag>LimitedThreadPool</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/Linked-List/ rel=tag>Linked List</a><span class=tag-list-count>2</span><li class=tag-list-item><a class=tag-list-link href=/tags/Lowest-Common-Ancestor-of-a-Binary-Tree/ rel=tag>Lowest Common Ancestor of a Binary Tree</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/MQ/ rel=tag>MQ</a><span class=tag-list-count>9</span><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 class=tag-list-item><a class=tag-list-link href=/tags/Maven/ rel=tag>Maven</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/Median-of-Two-Sorted-Arrays/ rel=tag>Median of Two Sorted Arrays</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/Mybatis/ rel=tag>Mybatis</a><span class=tag-list-count>13</span><li class=tag-list-item><a class=tag-list-link href=/tags/Mysql/ rel=tag>Mysql</a><span class=tag-list-count>13</span><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 class=tag-list-item><a class=tag-list-link href=/tags/PHP/ rel=tag>PHP</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/Preorder-Traversal/ rel=tag>Preorder Traversal</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/Print-FooBar-Alternately/ rel=tag>Print FooBar Alternately</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/RPC/ rel=tag>RPC</a><span class=tag-list-count>4</span><li class=tag-list-item><a class=tag-list-link href=/tags/Redis/ rel=tag>Redis</a><span class=tag-list-count>2</span><li class=tag-list-item><a class=tag-list-link href=/tags/Remove-Duplicates-from-Sorted-List/ rel=tag>Remove Duplicates from Sorted List</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/RocketMQ/ rel=tag>RocketMQ</a><span class=tag-list-count>9</span><li class=tag-list-item><a class=tag-list-link href=/tags/Rotate-Image/ rel=tag>Rotate Image</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/Rust/ rel=tag>Rust</a><span class=tag-list-count>3</span><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 class=tag-list-item><a class=tag-list-link href=/tags/Servlet/ rel=tag>Servlet</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/Sharding-Jdbc/ rel=tag>Sharding-Jdbc</a><span class=tag-list-count>3</span><li class=tag-list-item><a class=tag-list-link href=/tags/Shift-2D-Grid/ rel=tag>Shift 2D Grid</a><span class=tag-list-count>1</span><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 class=tag-list-item><a class=tag-list-link href=/tags/Spring/ rel=tag>Spring</a><span class=tag-list-count>7</span><li class=tag-list-item><a class=tag-list-link href=/tags/Spring-Event/ rel=tag>Spring Event</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/SpringBoot/ rel=tag>SpringBoot</a><span class=tag-list-count>22</span><li class=tag-list-item><a class=tag-list-link href=/tags/Sql%E6%B3%A8%E5%85%A5/ rel=tag>Sql注入</a><span class=tag-list-count>1</span><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 class=tag-list-item><a class=tag-list-link href=/tags/Synchronized/ rel=tag>Synchronized</a><span class=tag-list-count>2</span><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 class=tag-list-item><a class=tag-list-link href=/tags/ThreadLocal/ rel=tag>ThreadLocal</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/ThreadPool/ rel=tag>ThreadPool</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/Tomcat/ rel=tag>Tomcat</a><span class=tag-list-count>13</span><li class=tag-list-item><a class=tag-list-link href=/tags/Trapping-Rain-Water/ rel=tag>Trapping Rain Water</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/WeakReference/ rel=tag>WeakReference</a><span class=tag-list-count>1</span><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 class=tag-list-item><a class=tag-list-link href=/tags/Webhook/ rel=tag>Webhook</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/Windows/ rel=tag>Windows</a><span class=tag-list-count>5</span><li class=tag-list-item><a class=tag-list-link href=/tags/WordPress/ rel=tag>WordPress</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/aqs/ rel=tag>aqs</a><span class=tag-list-count>3</span><li class=tag-list-item><a class=tag-list-link href=/tags/await/ rel=tag>await</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/bloom-filter/ rel=tag>bloom filter</a><span class=tag-list-count>1</span><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 class=tag-list-item><a class=tag-list-link href=/tags/cglib/ rel=tag>cglib</a><span class=tag-list-count>1</span><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 class=tag-list-item><a class=tag-list-link href=/tags/cluster/ rel=tag>cluster</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/condition/ rel=tag>condition</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/dnsmasq/ rel=tag>dnsmasq</a><span class=tag-list-count>1</span><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 class=tag-list-item><a class=tag-list-link href=/tags/dp/ rel=tag>dp</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/dubbo/ rel=tag>dubbo</a><span class=tag-list-count>1</span><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 class=tag-list-item><a class=tag-list-link href=/tags/environment/ rel=tag>environment</a><span class=tag-list-count>2</span><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 class=tag-list-item><a class=tag-list-link href=/tags/gc/ rel=tag>gc</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/git/ rel=tag>git</a><span class=tag-list-count>4</span><li class=tag-list-item><a class=tag-list-link href=/tags/grep/ rel=tag>grep</a><span class=tag-list-count>3</span><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 class=tag-list-item><a class=tag-list-link href=/tags/headscale/ rel=tag>headscale</a><span class=tag-list-count>6</span><li class=tag-list-item><a class=tag-list-link href=/tags/hexo/ rel=tag>hexo</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/http/ rel=tag>http</a><span class=tag-list-count>1</span><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 class=tag-list-item><a class=tag-list-link href=/tags/im/ rel=tag>im</a><span class=tag-list-count>1</span><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 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 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 class=tag-list-item><a class=tag-list-link href=/tags/java/ rel=tag>java</a><span class=tag-list-count>48</span><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 class=tag-list-item><a class=tag-list-link href=/tags/leetcode/ rel=tag>leetcode</a><span class=tag-list-count>44</span><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 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 class=tag-list-item><a class=tag-list-link href=/tags/linux/ rel=tag>linux</a><span class=tag-list-count>6</span><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 class=tag-list-item><a class=tag-list-link href=/tags/mfc/ rel=tag>mfc</a><span class=tag-list-count>2</span><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 class=tag-list-item><a class=tag-list-link href=/tags/mq/ rel=tag>mq</a><span class=tag-list-count>1</span><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 class=tag-list-item><a class=tag-list-link href=/tags/mysql/ rel=tag>mysql</a><span class=tag-list-count>7</span><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 class=tag-list-item><a class=tag-list-link href=/tags/nas/ rel=tag>nas</a><span class=tag-list-count>6</span><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 class=tag-list-item><a class=tag-list-link href=/tags/nginx/ rel=tag>nginx</a><span class=tag-list-count>3</span><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 class=tag-list-item><a class=tag-list-link href=/tags/openresty/ rel=tag>openresty</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/openwrt/ rel=tag>openwrt</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/php/ rel=tag>php</a><span class=tag-list-count>5</span><li class=tag-list-item><a class=tag-list-link href=/tags/powershell/ rel=tag>powershell</a><span class=tag-list-count>2</span><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 class=tag-list-item><a class=tag-list-link href=/tags/python/ rel=tag>python</a><span class=tag-list-count>1</span><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 class=tag-list-item><a class=tag-list-link href=/tags/redis/ rel=tag>redis</a><span class=tag-list-count>12</span><li class=tag-list-item><a class=tag-list-link href=/tags/scp/ rel=tag>scp</a><span class=tag-list-count>1</span><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 class=tag-list-item><a class=tag-list-link href=/tags/sort/ rel=tag>sort</a><span class=tag-list-count>1</span><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 class=tag-list-item><a class=tag-list-link href=/tags/ssh/ rel=tag>ssh</a><span class=tag-list-count>3</span><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 class=tag-list-item><a class=tag-list-link href=/tags/stream/ rel=tag>stream</a><span class=tag-list-count>3</span><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 class=tag-list-item><a class=tag-list-link href=/tags/swoole/ rel=tag>swoole</a><span class=tag-list-count>1</span><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 class=tag-list-item><a class=tag-list-link href=/tags/uname/ rel=tag>uname</a><span class=tag-list-count>1</span><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 class=tag-list-item><a class=tag-list-link href=/tags/utf8/ rel=tag>utf8</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/utf8mb4/ rel=tag>utf8mb4</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/utf8mb4-0900-ai-ci/ rel=tag>utf8mb4_0900_ai_ci</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/utf8mb4-general-ci/ rel=tag>utf8mb4_general_ci</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/utf8mb4-unicode-ci/ rel=tag>utf8mb4_unicode_ci</a><span class=tag-list-count>1</span><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 class=tag-list-item><a class=tag-list-link href=/tags/websocket/ rel=tag>websocket</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/windows/ rel=tag>windows</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/wsl/ rel=tag>wsl</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/zookeeper/ rel=tag>zookeeper</a><span class=tag-list-count>1</span><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 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 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 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 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 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 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 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 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 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 class=tag-list-item><a class=tag-list-link href=/tags/%E4%BA%8B%E5%8A%A1/ rel=tag>事务</a><span class=tag-list-count>1</span><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 class=tag-list-item><a class=tag-list-link href=/tags/%E4%BA%91%E6%9C%8D%E5%8A%A1%E5%99%A8/ rel=tag>云服务器</a><span class=tag-list-count>1</span><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 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 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 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 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 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>3</span><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 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 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 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 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>7</span><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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 class=tag-list-item><a class=tag-list-link href=/tags/%E5%9B%A4%E7%89%A9%E8%B5%84/ rel=tag>囤物资</a><span class=tag-list-count>1</span><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 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 class=tag-list-item><a class=tag-list-link href=/tags/%E5%A4%A7%E6%89%AB%E9%99%A4/ rel=tag>大扫除</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E5%AD%97%E7%AC%A6%E9%9B%86/ rel=tag>字符集</a><span class=tag-list-count>1</span><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 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 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 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 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>9</span><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 class=tag-list-item><a class=tag-list-link href=/tags/%E5%B7%A5%E5%85%B7/ rel=tag>工具</a><span class=tag-list-count>2</span><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 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>6</span><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 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>4</span><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 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 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 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 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 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 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>2</span><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 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 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 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 class=tag-list-item><a class=tag-list-link href=/tags/%E6%8A%98%E8%85%BE/ rel=tag>折腾</a><span class=tag-list-count>3</span><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>2</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E6%8D%A2%E8%BD%A6%E7%89%8C/ rel=tag>换车牌</a><span class=tag-list-count>1</span><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 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 class=tag-list-item><a class=tag-list-link href=/tags/%E6%95%B0%E6%8D%AE%E6%BA%90%E5%8A%A8%E6%80%81%E5%88%87%E6%8D%A2/ rel=tag>数据源动态切换</a><span class=tag-list-count>1</span><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 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 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 class=tag-list-item><a class=tag-list-link href=/tags/%E6%97%A5%E5%BF%97/ rel=tag>日志</a><span class=tag-list-count>1</span><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 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 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 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>4</span><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 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 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 class=tag-list-item><a class=tag-list-link href=/tags/%E6%B3%A8%E8%A7%A3/ rel=tag>注解</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E6%B5%B7%E8%9B%8E%E7%85%8E/ rel=tag>海蛎煎</a><span class=tag-list-count>1</span><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>9</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E6%B7%98%E6%B1%B0%E7%AD%96%E7%95%A5/ rel=tag>淘汰策略</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E6%B7%B1%E5%BA%A6%E5%AD%A6%E4%B9%A0/ rel=tag>深度学习</a><span class=tag-list-count>1</span><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 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 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>42</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E7%94%B5%E7%93%B6%E8%BD%A6/ rel=tag>电瓶车</a><span class=tag-list-count>2</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E7%96%AB%E6%83%85/ rel=tag>疫情</a><span class=tag-list-count>2</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E7%9C%8B%E4%B9%A6/ rel=tag>看书</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E7%9C%8B%E5%89%A7/ rel=tag>看剧</a><span class=tag-list-count>3</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E7%9F%A9%E9%98%B5/ rel=tag>矩阵</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E7%AB%AF%E5%8F%A3%E8%BD%AC%E5%8F%91/ rel=tag>端口转发</a><span class=tag-list-count>3</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E7%AE%97%E6%B3%95/ rel=tag>算法</a><span class=tag-list-count>5</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E7%B1%BB%E5%8A%A0%E8%BD%BD/ rel=tag>类加载</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E7%B3%9F%E5%BF%83%E4%BA%8B/ rel=tag>糟心事</a><span class=tag-list-count>5</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E7%B4%A2%E5%BC%95/ rel=tag>索引</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E7%BA%BF%E7%A8%8B%E6%B1%A0/ rel=tag>线程池</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E7%BC%93%E5%AD%98/ rel=tag>缓存</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E7%BC%93%E5%AD%98%E5%87%BB%E7%A9%BF/ rel=tag>缓存击穿</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E7%BC%93%E5%AD%98%E7%A9%BF%E9%80%8F/ rel=tag>缓存穿透</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E7%BC%93%E5%AD%98%E9%9B%AA%E5%B4%A9/ rel=tag>缓存雪崩</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E7%BC%96%E7%A0%81/ rel=tag>编码</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E7%BE%8E%E5%9B%BD/ rel=tag>美国</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E8%80%81%E7%94%B5%E8%84%91/ rel=tag>老电脑</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E8%87%AA%E5%8A%A8%E8%A3%85%E9%85%8D/ rel=tag>自动装配</a><span class=tag-list-count>2</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E8%87%AA%E6%97%8B/ rel=tag>自旋</a><span class=tag-list-count>2</span><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 class=tag-list-item><a class=tag-list-link href=/tags/%E8%A3%85%E7%94%B5%E8%84%91/ rel=tag>装电脑</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E8%A7%84%E5%88%99/ rel=tag>规则</a><span class=tag-list-count>4</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E8%A7%A3%E6%9E%90/ rel=tag>解析</a><span class=tag-list-count>1</span><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 class=tag-list-item><a class=tag-list-link href=/tags/%E8%AF%BB%E4%B9%A6/ rel=tag>读书</a><span class=tag-list-count>2</span><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>4</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E8%B4%9F%E8%BD%BD%E5%9D%87%E8%A1%A1/ rel=tag>负载均衡</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E8%B6%B3%E7%90%83/ rel=tag>足球</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link 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class=post-content itemscope itemtype=http://schema.org/Article lang=zh-CN><link href=https://nicksxs.me/2020/04/12/redis%E7%B3%BB%E5%88%97%E4%BB%8B%E7%BB%8D%E4%B8%83/ itemprop=mainEntityOfPage><span hidden itemprop=author itemscope itemtype=http://schema.org/Person><meta content=/uploads/avatar.jpg itemprop=image><meta content=Nicksxs itemprop=name></span><span hidden itemprop=publisher itemscope itemtype=http://schema.org/Organization><meta content="Nicksxs's Blog" itemprop=name><meta content="learn from zero,技术博客，Nicksxs，史学森" itemprop=description></span><span hidden itemprop=post itemscope itemtype=http://schema.org/CreativeWork><meta content="redis系列介绍七-过期策略 | Nicksxs's Blog" itemprop=name><meta itemprop=description></span><header class=post-header><h1 itemprop="name headline" class=post-title>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>发表于</span> <time itemprop="dateCreated datePublished" title="创建时间：2020-04-12 21:22:00 / 修改时间：22:57:42" 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>分类于</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 class="post-meta-item leancloud_visitors" data-flag-title=redis系列介绍七-过期策略 id=/2020/04/12/redis%E7%B3%BB%E5%88%97%E4%BB%8B%E7%BB%8D%E4%B8%83/ title=阅读次数><span class=post-meta-item-icon><i class="far fa-eye"></i> </span><span class=post-meta-item-text>阅读次数：</span> <span class=leancloud-visitors-count></span> </span><span class=post-meta-item id=busuanzi_container_page_pv title=阅读次数><span class=post-meta-item-icon><i class="far fa-eye"></i> </span><span class=post-meta-item-text>阅读次数：</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 href=/2020/04/12/redis%E7%B3%BB%E5%88%97%E4%BB%8B%E7%BB%8D%E4%B8%83/#disqus_thread itemprop=discussionUrl title=disqus><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，<h2 id=redis过期策略><a class=headerlink href=#redis过期策略 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<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></pre><td class=code><pre><span class=line><span class=comment>/* This function is called when we are going to perform some operation</span></span><br><span class=line><span class=comment> * in a given key, but such key may be already logically expired even if</span></span><br><span class=line><span class=comment> * it still exists in the database. The main way this function is called</span></span><br><span class=line><span class=comment> * is via lookupKey*() family of functions.</span></span><br><span class=line><span class=comment> *</span></span><br><span class=line><span class=comment> * The behavior of the function depends on the replication role of the</span></span><br><span class=line><span class=comment> * instance, because slave instances do not expire keys, they wait</span></span><br><span class=line><span class=comment> * for DELs from the master for consistency matters. However even</span></span><br><span class=line><span class=comment> * slaves will try to have a coherent return value for the function,</span></span><br><span class=line><span class=comment> * so that read commands executed in the slave side will be able to</span></span><br><span class=line><span class=comment> * behave like if the key is expired even if still present (because the</span></span><br><span class=line><span class=comment> * master has yet to propagate the DEL).</span></span><br><span class=line><span class=comment> *</span></span><br><span class=line><span class=comment> * In masters as a side effect of finding a key which is expired, such</span></span><br><span class=line><span class=comment> * key will be evicted from the database. Also this may trigger the</span></span><br><span class=line><span class=comment> * propagation of a DEL/UNLINK command in AOF / replication stream.</span></span><br><span class=line><span class=comment> *</span></span><br><span class=line><span class=comment> * The return value of the function is 0 if the key is still valid,</span></span><br><span class=line><span class=comment> * otherwise the function returns 1 if the key is expired. */</span></span><br><span class=line><span class=type>int</span> <span class="title function_">expireIfNeeded</span><span class=params>(redisDb *db, robj *key)</span> {</span><br><span class=line> <span class=keyword>if</span> (!keyIsExpired(db,key)) <span class=keyword>return</span> <span class=number>0</span>;</span><br><span class=line></span><br><span class=line> <span class=comment>/* If we are running in the context of a slave, instead of</span></span><br><span class=line><span class=comment> * evicting the expired key from the database, we return ASAP:</span></span><br><span class=line><span class=comment> * the slave key expiration is controlled by the master that will</span></span><br><span class=line><span class=comment> * send us synthesized DEL operations for expired keys.</span></span><br><span class=line><span class=comment> *</span></span><br><span class=line><span class=comment> * Still we try to return the right information to the caller,</span></span><br><span class=line><span class=comment> * that is, 0 if we think the key should be still valid, 1 if</span></span><br><span class=line><span class=comment> * we think the key is expired at this time. */</span></span><br><span class=line> <span class=keyword>if</span> (server.masterhost != <span class=literal>NULL</span>) <span class=keyword>return</span> <span class=number>1</span>;</span><br><span class=line></span><br><span class=line> <span class=comment>/* Delete the key */</span></span><br><span class=line> server.stat_expiredkeys++;</span><br><span class=line> propagateExpire(db,key,server.lazyfree_lazy_expire);</span><br><span class=line> notifyKeyspaceEvent(NOTIFY_EXPIRED,</span><br><span class=line> <span class=string>"expired"</span>,key,db->id);</span><br><span class=line> <span class=keyword>return</span> server.lazyfree_lazy_expire ? dbAsyncDelete(db,key) :</span><br><span class=line> dbSyncDelete(db,key);</span><br><span class=line>}</span><br><span class=line></span><br><span class=line><span class=comment>/* Check if the key is expired. */</span></span><br><span class=line><span class=type>int</span> <span class="title function_">keyIsExpired</span><span class=params>(redisDb *db, robj *key)</span> {</span><br><span class=line> <span class=type>mstime_t</span> when = getExpire(db,key);</span><br><span class=line> <span class=type>mstime_t</span> now;</span><br><span class=line></span><br><span class=line> <span class=keyword>if</span> (when < <span class=number>0</span>) <span class=keyword>return</span> <span class=number>0</span>; <span class=comment>/* No expire for this key */</span></span><br><span class=line></span><br><span class=line> <span class=comment>/* Don't expire anything while loading. It will be done later. */</span></span><br><span class=line> <span class=keyword>if</span> (server.loading) <span class=keyword>return</span> <span class=number>0</span>;</span><br><span class=line></span><br><span class=line> <span class=comment>/* If we are in the context of a Lua script, we pretend that time is</span></span><br><span class=line><span class=comment> * blocked to when the Lua script started. This way a key can expire</span></span><br><span class=line><span class=comment> * only the first time it is accessed and not in the middle of the</span></span><br><span class=line><span class=comment> * script execution, making propagation to slaves / AOF consistent.</span></span><br><span class=line><span class=comment> * See issue #1525 on Github for more information. */</span></span><br><span class=line> <span class=keyword>if</span> (server.lua_caller) {</span><br><span class=line> now = server.lua_time_start;</span><br><span class=line> }</span><br><span class=line> <span class=comment>/* If we are in the middle of a command execution, we still want to use</span></span><br><span class=line><span class=comment> * a reference time that does not change: in that case we just use the</span></span><br><span class=line><span class=comment> * cached time, that we update before each call in the call() function.</span></span><br><span class=line><span class=comment> * This way we avoid that commands such as RPOPLPUSH or similar, that</span></span><br><span class=line><span class=comment> * may re-open the same key multiple times, can invalidate an already</span></span><br><span class=line><span class=comment> * open object in a next call, if the next call will see the key expired,</span></span><br><span class=line><span class=comment> * while the first did not. */</span></span><br><span class=line> <span class=keyword>else</span> <span class=keyword>if</span> (server.fixed_time_expire > <span class=number>0</span>) {</span><br><span class=line> now = server.mstime;</span><br><span class=line> }</span><br><span class=line> <span class=comment>/* For the other cases, we want to use the most fresh time we have. */</span></span><br><span class=line> <span class=keyword>else</span> {</span><br><span class=line> now = mstime();</span><br><span class=line> }</span><br><span class=line></span><br><span class=line> <span class=comment>/* The key expired if the current (virtual or real) time is greater</span></span><br><span class=line><span class=comment> * than the expire time of the key. */</span></span><br><span class=line> <span class=keyword>return</span> now > when;</span><br><span class=line>}</span><br><span class=line><span class=comment>/* Return the expire time of the specified key, or -1 if no expire</span></span><br><span class=line><span class=comment> * is associated with this key (i.e. the key is non volatile) */</span></span><br><span class=line><span class=type>long</span> <span class=type>long</span> <span class="title function_">getExpire</span><span class=params>(redisDb *db, robj *key)</span> {</span><br><span class=line> dictEntry *de;</span><br><span class=line></span><br><span class=line> <span class=comment>/* No expire? return ASAP */</span></span><br><span class=line> <span class=keyword>if</span> (dictSize(db->expires) == <span class=number>0</span> ||</span><br><span class=line> (de = dictFind(db->expires,key->ptr)) == <span class=literal>NULL</span>) <span class=keyword>return</span> <span class=number>-1</span>;</span><br><span class=line></span><br><span class=line> <span class=comment>/* The entry was found in the expire dict, this means it should also</span></span><br><span class=line><span class=comment> * be present in the main dict (safety check). */</span></span><br><span class=line> serverAssertWithInfo(<span class=literal>NULL</span>,key,dictFind(db->dict,key->ptr) != <span class=literal>NULL</span>);</span><br><span class=line> <span class=keyword>return</span> dictGetSignedIntegerVal(de);</span><br><span class=line>}</span><br></pre></table></figure><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<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><span class=line>198</span><br><span class=line>199</span><br><span class=line>200</span><br><span class=line>201</span><br><span class=line>202</span><br><span class=line>203</span><br><span class=line>204</span><br><span class=line>205</span><br><span class=line>206</span><br><span class=line>207</span><br><span class=line>208</span><br><span class=line>209</span><br><span class=line>210</span><br><span class=line>211</span><br><span class=line>212</span><br><span class=line>213</span><br><span class=line>214</span><br><span class=line>215</span><br><span class=line>216</span><br><span class=line>217</span><br><span class=line>218</span><br><span class=line>219</span><br><span class=line>220</span><br><span class=line>221</span><br><span class=line>222</span><br><span class=line>223</span><br><span class=line>224</span><br><span class=line>225</span><br><span class=line>226</span><br><span class=line>227</span><br><span class=line>228</span><br><span class=line>229</span><br><span class=line>230</span><br><span class=line>231</span><br><span class=line>232</span><br><span class=line>233</span><br><span class=line>234</span><br><span class=line>235</span><br><span class=line>236</span><br><span class=line>237</span><br><span class=line>238</span><br><span class=line>239</span><br><span class=line>240</span><br><span class=line>241</span><br><span class=line>242</span><br><span class=line>243</span><br><span class=line>244</span><br><span class=line>245</span><br><span class=line>246</span><br><span class=line>247</span><br><span class=line>248</span><br><span class=line>249</span><br><span class=line>250</span><br><span class=line>251</span><br><span class=line>252</span><br><span class=line>253</span><br><span class=line>254</span><br><span class=line>255</span><br><span class=line>256</span><br><span class=line>257</span><br><span class=line>258</span><br><span class=line>259</span><br><span class=line>260</span><br><span class=line>261</span><br><span class=line>262</span><br><span class=line>263</span><br><span class=line>264</span><br><span class=line>265</span><br><span class=line>266</span><br><span class=line>267</span><br><span class=line>268</span><br><span class=line>269</span><br><span class=line>270</span><br><span class=line>271</span><br><span class=line>272</span><br><span class=line>273</span><br><span class=line>274</span><br><span class=line>275</span><br><span class=line>276</span><br><span class=line>277</span><br><span class=line>278</span><br><span class=line>279</span><br><span class=line>280</span><br><span class=line>281</span><br><span class=line>282</span><br><span class=line>283</span><br><span class=line>284</span><br><span class=line>285</span><br><span class=line>286</span><br><span class=line>287</span><br><span class=line>288</span><br><span class=line>289</span><br><span class=line>290</span><br><span class=line>291</span><br><span class=line>292</span><br><span class=line>293</span><br><span class=line>294</span><br><span class=line>295</span><br><span class=line>296</span><br><span class=line>297</span><br><span class=line>298</span><br><span class=line>299</span><br><span class=line>300</span><br><span class=line>301</span><br><span class=line>302</span><br><span class=line>303</span><br><span class=line>304</span><br></pre><td class=code><pre><span class=line><span class=comment>/* This function handles 'background' operations we are required to do</span></span><br><span class=line><span class=comment> * incrementally in Redis databases, such as active key expiring, resizing,</span></span><br><span class=line><span class=comment> * rehashing. */</span></span><br><span class=line><span class=type>void</span> <span class="title function_">databasesCron</span><span class=params>(<span class=type>void</span>)</span> {</span><br><span class=line> <span class=comment>/* Expire keys by random sampling. Not required for slaves</span></span><br><span class=line><span class=comment> * as master will synthesize DELs for us. */</span></span><br><span class=line> <span class=keyword>if</span> (server.active_expire_enabled) {</span><br><span class=line> <span class=keyword>if</span> (server.masterhost == <span class=literal>NULL</span>) {</span><br><span class=line> activeExpireCycle(ACTIVE_EXPIRE_CYCLE_SLOW);</span><br><span class=line> } <span class=keyword>else</span> {</span><br><span class=line> expireSlaveKeys();</span><br><span class=line> }</span><br><span class=line> }</span><br><span class=line></span><br><span class=line> <span class=comment>/* Defrag keys gradually. */</span></span><br><span class=line> activeDefragCycle();</span><br><span class=line></span><br><span class=line> <span class=comment>/* Perform hash tables rehashing if needed, but only if there are no</span></span><br><span class=line><span class=comment> * other processes saving the DB on disk. Otherwise rehashing is bad</span></span><br><span class=line><span class=comment> * as will cause a lot of copy-on-write of memory pages. */</span></span><br><span class=line> <span class=keyword>if</span> (!hasActiveChildProcess()) {</span><br><span class=line> <span class=comment>/* We use global counters so if we stop the computation at a given</span></span><br><span class=line><span class=comment> * DB we'll be able to start from the successive in the next</span></span><br><span class=line><span class=comment> * cron loop iteration. */</span></span><br><span class=line> <span class=type>static</span> <span class=type>unsigned</span> <span class=type>int</span> resize_db = <span class=number>0</span>;</span><br><span class=line> <span class=type>static</span> <span class=type>unsigned</span> <span class=type>int</span> rehash_db = <span class=number>0</span>;</span><br><span class=line> <span class=type>int</span> dbs_per_call = CRON_DBS_PER_CALL;</span><br><span class=line> <span class=type>int</span> j;</span><br><span class=line></span><br><span class=line> <span class=comment>/* Don't test more DBs than we have. */</span></span><br><span class=line> <span class=keyword>if</span> (dbs_per_call > server.dbnum) dbs_per_call = server.dbnum;</span><br><span class=line></span><br><span class=line> <span class=comment>/* Resize */</span></span><br><span class=line> <span class=keyword>for</span> (j = <span class=number>0</span>; j < dbs_per_call; j++) {</span><br><span class=line> tryResizeHashTables(resize_db % server.dbnum);</span><br><span class=line> resize_db++;</span><br><span class=line> }</span><br><span class=line></span><br><span class=line> <span class=comment>/* Rehash */</span></span><br><span class=line> <span class=keyword>if</span> (server.activerehashing) {</span><br><span class=line> <span class=keyword>for</span> (j = <span class=number>0</span>; j < dbs_per_call; j++) {</span><br><span class=line> <span class=type>int</span> work_done = incrementallyRehash(rehash_db);</span><br><span class=line> <span class=keyword>if</span> (work_done) {</span><br><span class=line> <span class=comment>/* If the function did some work, stop here, we'll do</span></span><br><span class=line><span class=comment> * more at the next cron loop. */</span></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>/* If this db didn't need rehash, we'll try the next one. */</span></span><br><span class=line> rehash_db++;</span><br><span class=line> rehash_db %= server.dbnum;</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>/* Try to expire a few timed out keys. The algorithm used is adaptive and</span></span><br><span class=line><span class=comment> * will use few CPU cycles if there are few expiring keys, otherwise</span></span><br><span class=line><span class=comment> * it will get more aggressive to avoid that too much memory is used by</span></span><br><span class=line><span class=comment> * keys that can be removed from the keyspace.</span></span><br><span class=line><span class=comment> *</span></span><br><span class=line><span class=comment> * Every expire cycle tests multiple databases: the next call will start</span></span><br><span class=line><span class=comment> * again from the next db, with the exception of exists for time limit: in that</span></span><br><span class=line><span class=comment> * case we restart again from the last database we were processing. Anyway</span></span><br><span class=line><span class=comment> * no more than CRON_DBS_PER_CALL databases are tested at every iteration.</span></span><br><span class=line><span class=comment> *</span></span><br><span class=line><span class=comment> * The function can perform more or less work, depending on the "type"</span></span><br><span class=line><span class=comment> * argument. It can execute a "fast cycle" or a "slow cycle". The slow</span></span><br><span class=line><span class=comment> * cycle is the main way we collect expired cycles: this happens with</span></span><br><span class=line><span class=comment> * the "server.hz" frequency (usually 10 hertz).</span></span><br><span class=line><span class=comment> *</span></span><br><span class=line><span class=comment> * However the slow cycle can exit for timeout, since it used too much time.</span></span><br><span class=line><span class=comment> * For this reason the function is also invoked to perform a fast cycle</span></span><br><span class=line><span class=comment> * at every event loop cycle, in the beforeSleep() function. The fast cycle</span></span><br><span class=line><span class=comment> * will try to perform less work, but will do it much more often.</span></span><br><span class=line><span class=comment> *</span></span><br><span class=line><span class=comment> * The following are the details of the two expire cycles and their stop</span></span><br><span class=line><span class=comment> * conditions:</span></span><br><span class=line><span class=comment> *</span></span><br><span class=line><span class=comment> * If type is ACTIVE_EXPIRE_CYCLE_FAST the function will try to run a</span></span><br><span class=line><span class=comment> * "fast" expire cycle that takes no longer than EXPIRE_FAST_CYCLE_DURATION</span></span><br><span class=line><span class=comment> * microseconds, and is not repeated again before the same amount of time.</span></span><br><span class=line><span class=comment> * The cycle will also refuse to run at all if the latest slow cycle did not</span></span><br><span class=line><span class=comment> * terminate because of a time limit condition.</span></span><br><span class=line><span class=comment> *</span></span><br><span class=line><span class=comment> * If type is ACTIVE_EXPIRE_CYCLE_SLOW, that normal expire cycle is</span></span><br><span class=line><span class=comment> * executed, where the time limit is a percentage of the REDIS_HZ period</span></span><br><span class=line><span class=comment> * as specified by the ACTIVE_EXPIRE_CYCLE_SLOW_TIME_PERC define. In the</span></span><br><span class=line><span class=comment> * fast cycle, the check of every database is interrupted once the number</span></span><br><span class=line><span class=comment> * of already expired keys in the database is estimated to be lower than</span></span><br><span class=line><span class=comment> * a given percentage, in order to avoid doing too much work to gain too</span></span><br><span class=line><span class=comment> * little memory.</span></span><br><span class=line><span class=comment> *</span></span><br><span class=line><span class=comment> * The configured expire "effort" will modify the baseline parameters in</span></span><br><span class=line><span class=comment> * order to do more work in both the fast and slow expire cycles.</span></span><br><span class=line><span class=comment> */</span></span><br><span class=line></span><br><span class=line><span class=meta>#<span class=keyword>define</span> ACTIVE_EXPIRE_CYCLE_KEYS_PER_LOOP 20 <span class=comment>/* Keys for each DB loop. */</span></span></span><br><span class=line><span class=meta>#<span class=keyword>define</span> ACTIVE_EXPIRE_CYCLE_FAST_DURATION 1000 <span class=comment>/* Microseconds. */</span></span></span><br><span class=line><span class=meta>#<span class=keyword>define</span> ACTIVE_EXPIRE_CYCLE_SLOW_TIME_PERC 25 <span class=comment>/* Max % of CPU to use. */</span></span></span><br><span class=line><span class=meta>#<span class=keyword>define</span> ACTIVE_EXPIRE_CYCLE_ACCEPTABLE_STALE 10 <span class=comment>/* % of stale keys after which</span></span></span><br><span class=line><span class=comment><span class=meta> we do extra efforts. */</span></span></span><br><span class=line><span class=type>void</span> <span class="title function_">activeExpireCycle</span><span class=params>(<span class=type>int</span> type)</span> {</span><br><span class=line> <span class=comment>/* Adjust the running parameters according to the configured expire</span></span><br><span class=line><span class=comment> * effort. The default effort is 1, and the maximum configurable effort</span></span><br><span class=line><span class=comment> * is 10. */</span></span><br><span class=line> <span class=type>unsigned</span> <span class=type>long</span></span><br><span class=line> effort = server.active_expire_effort<span class=number>-1</span>, <span class=comment>/* Rescale from 0 to 9. */</span></span><br><span class=line> config_keys_per_loop = ACTIVE_EXPIRE_CYCLE_KEYS_PER_LOOP +</span><br><span class=line> ACTIVE_EXPIRE_CYCLE_KEYS_PER_LOOP/<span class=number>4</span>*effort,</span><br><span class=line> config_cycle_fast_duration = ACTIVE_EXPIRE_CYCLE_FAST_DURATION +</span><br><span class=line> ACTIVE_EXPIRE_CYCLE_FAST_DURATION/<span class=number>4</span>*effort,</span><br><span class=line> config_cycle_slow_time_perc = ACTIVE_EXPIRE_CYCLE_SLOW_TIME_PERC +</span><br><span class=line> <span class=number>2</span>*effort,</span><br><span class=line> config_cycle_acceptable_stale = ACTIVE_EXPIRE_CYCLE_ACCEPTABLE_STALE-</span><br><span class=line> effort;</span><br><span class=line></span><br><span class=line> <span class=comment>/* This function has some global state in order to continue the work</span></span><br><span class=line><span class=comment> * incrementally across calls. */</span></span><br><span class=line> <span class=type>static</span> <span class=type>unsigned</span> <span class=type>int</span> current_db = <span class=number>0</span>; <span class=comment>/* Last DB tested. */</span></span><br><span class=line> <span class=type>static</span> <span class=type>int</span> timelimit_exit = <span class=number>0</span>; <span class=comment>/* Time limit hit in previous call? */</span></span><br><span class=line> <span class=type>static</span> <span class=type>long</span> <span class=type>long</span> last_fast_cycle = <span class=number>0</span>; <span class=comment>/* When last fast cycle ran. */</span></span><br><span class=line></span><br><span class=line> <span class=type>int</span> j, iteration = <span class=number>0</span>;</span><br><span class=line> <span class=type>int</span> dbs_per_call = CRON_DBS_PER_CALL;</span><br><span class=line> <span class=type>long</span> <span class=type>long</span> start = ustime(), timelimit, elapsed;</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>;</span><br><span class=line></span><br><span class=line> <span class=keyword>if</span> (type == ACTIVE_EXPIRE_CYCLE_FAST) {</span><br><span class=line> <span class=comment>/* Don't start a fast cycle if the previous cycle did not exit</span></span><br><span class=line><span class=comment> * for time limit, unless the percentage of estimated stale keys is</span></span><br><span class=line><span class=comment> * too high. Also never repeat a fast cycle for the same period</span></span><br><span class=line><span class=comment> * as the fast cycle total duration itself. */</span></span><br><span class=line> <span class=keyword>if</span> (!timelimit_exit &&</span><br><span class=line> server.stat_expired_stale_perc < config_cycle_acceptable_stale)</span><br><span class=line> <span class=keyword>return</span>;</span><br><span class=line></span><br><span class=line> <span class=keyword>if</span> (start < last_fast_cycle + (<span class=type>long</span> <span class=type>long</span>)config_cycle_fast_duration*<span class=number>2</span>)</span><br><span class=line> <span class=keyword>return</span>;</span><br><span class=line></span><br><span class=line> last_fast_cycle = start;</span><br><span class=line> }</span><br><span class=line></span><br><span class=line> <span class=comment>/* We usually should test CRON_DBS_PER_CALL per iteration, with</span></span><br><span class=line><span class=comment> * two exceptions:</span></span><br><span class=line><span class=comment> *</span></span><br><span class=line><span class=comment> * 1) Don't test more DBs than we have.</span></span><br><span class=line><span class=comment> * 2) If last time we hit the time limit, we want to scan all DBs</span></span><br><span class=line><span class=comment> * in this iteration, as there is work to do in some DB and we don't want</span></span><br><span class=line><span class=comment> * expired keys to use memory for too much time. */</span></span><br><span class=line> <span class=keyword>if</span> (dbs_per_call > server.dbnum || timelimit_exit)</span><br><span class=line> dbs_per_call = server.dbnum;</span><br><span class=line></span><br><span class=line> <span class=comment>/* We can use at max 'config_cycle_slow_time_perc' percentage of CPU</span></span><br><span class=line><span class=comment> * time per iteration. Since this function gets called with a frequency of</span></span><br><span class=line><span class=comment> * server.hz times per second, the following is the max amount of</span></span><br><span class=line><span class=comment> * microseconds we can spend in this function. */</span></span><br><span class=line> timelimit = config_cycle_slow_time_perc*<span class=number>1000000</span>/server.hz/<span class=number>100</span>;</span><br><span class=line> timelimit_exit = <span class=number>0</span>;</span><br><span class=line> <span class=keyword>if</span> (timelimit <= <span class=number>0</span>) timelimit = <span class=number>1</span>;</span><br><span class=line></span><br><span class=line> <span class=keyword>if</span> (type == ACTIVE_EXPIRE_CYCLE_FAST)</span><br><span class=line> timelimit = config_cycle_fast_duration; <span class=comment>/* in microseconds. */</span></span><br><span class=line></span><br><span class=line> <span class=comment>/* Accumulate some global stats as we expire keys, to have some idea</span></span><br><span class=line><span class=comment> * about the number of keys that are already logically expired, but still</span></span><br><span class=line><span class=comment> * existing inside the database. */</span></span><br><span class=line> <span class=type>long</span> total_sampled = <span class=number>0</span>;</span><br><span class=line> <span class=type>long</span> total_expired = <span class=number>0</span>;</span><br><span class=line></span><br><span class=line> <span class=keyword>for</span> (j = <span class=number>0</span>; j < dbs_per_call && timelimit_exit == <span class=number>0</span>; j++) {</span><br><span class=line> <span class=comment>/* Expired and checked in a single loop. */</span></span><br><span class=line> <span class=type>unsigned</span> <span class=type>long</span> expired, sampled;</span><br><span class=line></span><br><span class=line> redisDb *db = server.db+(current_db % server.dbnum);</span><br><span class=line></span><br><span class=line> <span class=comment>/* Increment the DB now so we are sure if we run out of time</span></span><br><span class=line><span class=comment> * in the current DB we'll restart from the next. This allows to</span></span><br><span class=line><span class=comment> * distribute the time evenly across DBs. */</span></span><br><span class=line> current_db++;</span><br><span class=line></span><br><span class=line> <span class=comment>/* Continue to expire if at the end of the cycle more than 25%</span></span><br><span class=line><span class=comment> * of the keys were expired. */</span></span><br><span class=line> <span class=keyword>do</span> {</span><br><span class=line> <span class=type>unsigned</span> <span class=type>long</span> num, slots;</span><br><span class=line> <span class=type>long</span> <span class=type>long</span> now, ttl_sum;</span><br><span class=line> <span class=type>int</span> ttl_samples;</span><br><span class=line> iteration++;</span><br><span class=line></span><br><span class=line> <span class=comment>/* If there is nothing to expire try next DB ASAP. */</span></span><br><span class=line> <span class=keyword>if</span> ((num = dictSize(db->expires)) == <span class=number>0</span>) {</span><br><span class=line> db->avg_ttl = <span class=number>0</span>;</span><br><span class=line> <span class=keyword>break</span>;</span><br><span class=line> }</span><br><span class=line> slots = dictSlots(db->expires);</span><br><span class=line> now = mstime();</span><br><span class=line></span><br><span class=line> <span class=comment>/* When there are less than 1% filled slots, sampling the key</span></span><br><span class=line><span class=comment> * space is expensive, so stop here waiting for better times...</span></span><br><span class=line><span class=comment> * The dictionary will be resized asap. */</span></span><br><span class=line> <span class=keyword>if</span> (num && slots > DICT_HT_INITIAL_SIZE &&</span><br><span class=line> (num*<span class=number>100</span>/slots < <span class=number>1</span>)) <span class=keyword>break</span>;</span><br><span class=line></span><br><span class=line> <span class=comment>/* The main collection cycle. Sample random keys among keys</span></span><br><span class=line><span class=comment> * with an expire set, checking for expired ones. */</span></span><br><span class=line> expired = <span class=number>0</span>;</span><br><span class=line> sampled = <span class=number>0</span>;</span><br><span class=line> ttl_sum = <span class=number>0</span>;</span><br><span class=line> ttl_samples = <span class=number>0</span>;</span><br><span class=line></span><br><span class=line> <span class=keyword>if</span> (num > config_keys_per_loop)</span><br><span class=line> num = config_keys_per_loop;</span><br><span class=line></span><br><span class=line> <span class=comment>/* Here we access the low level representation of the hash table</span></span><br><span class=line><span class=comment> * for speed concerns: this makes this code coupled with dict.c,</span></span><br><span class=line><span class=comment> * but it hardly changed in ten years.</span></span><br><span class=line><span class=comment> *</span></span><br><span class=line><span class=comment> * Note that certain places of the hash table may be empty,</span></span><br><span class=line><span class=comment> * so we want also a stop condition about the number of</span></span><br><span class=line><span class=comment> * buckets that we scanned. However scanning for free buckets</span></span><br><span class=line><span class=comment> * is very fast: we are in the cache line scanning a sequential</span></span><br><span class=line><span class=comment> * array of NULL pointers, so we can scan a lot more buckets</span></span><br><span class=line><span class=comment> * than keys in the same time. */</span></span><br><span class=line> <span class=type>long</span> max_buckets = num*<span class=number>20</span>;</span><br><span class=line> <span class=type>long</span> checked_buckets = <span class=number>0</span>;</span><br><span class=line></span><br><span class=line> <span class=keyword>while</span> (sampled < num && checked_buckets < max_buckets) {</span><br><span class=line> <span class=keyword>for</span> (<span class=type>int</span> table = <span class=number>0</span>; table < <span class=number>2</span>; table++) {</span><br><span class=line> <span class=keyword>if</span> (table == <span class=number>1</span> && !dictIsRehashing(db->expires)) <span class=keyword>break</span>;</span><br><span class=line></span><br><span class=line> <span class=type>unsigned</span> <span class=type>long</span> idx = db->expires_cursor;</span><br><span class=line> idx &= db->expires->ht[table].sizemask;</span><br><span class=line> dictEntry *de = db->expires->ht[table].table[idx];</span><br><span class=line> <span class=type>long</span> <span class=type>long</span> ttl;</span><br><span class=line></span><br><span class=line> <span class=comment>/* Scan the current bucket of the current table. */</span></span><br><span class=line> checked_buckets++;</span><br><span class=line> <span class=keyword>while</span>(de) {</span><br><span class=line> <span class=comment>/* Get the next entry now since this entry may get</span></span><br><span class=line><span class=comment> * deleted. */</span></span><br><span class=line> dictEntry *e = de;</span><br><span class=line> de = de->next;</span><br><span class=line></span><br><span class=line> ttl = dictGetSignedIntegerVal(e)-now;</span><br><span class=line> <span class=keyword>if</span> (activeExpireCycleTryExpire(db,e,now)) expired++;</span><br><span class=line> <span class=keyword>if</span> (ttl > <span class=number>0</span>) {</span><br><span class=line> <span class=comment>/* We want the average TTL of keys yet</span></span><br><span class=line><span class=comment> * not expired. */</span></span><br><span class=line> ttl_sum += ttl;</span><br><span class=line> ttl_samples++;</span><br><span class=line> }</span><br><span class=line> sampled++;</span><br><span class=line> }</span><br><span class=line> }</span><br><span class=line> db->expires_cursor++;</span><br><span class=line> }</span><br><span class=line> total_expired += expired;</span><br><span class=line> total_sampled += sampled;</span><br><span class=line></span><br><span class=line> <span class=comment>/* Update the average TTL stats for this database. */</span></span><br><span class=line> <span class=keyword>if</span> (ttl_samples) {</span><br><span class=line> <span class=type>long</span> <span class=type>long</span> avg_ttl = ttl_sum/ttl_samples;</span><br><span class=line></span><br><span class=line> <span class=comment>/* Do a simple running average with a few samples.</span></span><br><span class=line><span class=comment> * We just use the current estimate with a weight of 2%</span></span><br><span class=line><span class=comment> * and the previous estimate with a weight of 98%. */</span></span><br><span class=line> <span class=keyword>if</span> (db->avg_ttl == <span class=number>0</span>) db->avg_ttl = avg_ttl;</span><br><span class=line> db->avg_ttl = (db->avg_ttl/<span class=number>50</span>)*<span class=number>49</span> + (avg_ttl/<span class=number>50</span>);</span><br><span class=line> }</span><br><span class=line></span><br><span class=line> <span class=comment>/* We can't block forever here even if there are many keys to</span></span><br><span class=line><span class=comment> * expire. So after a given amount of milliseconds return to the</span></span><br><span class=line><span class=comment> * caller waiting for the other active expire cycle. */</span></span><br><span class=line> <span class=keyword>if</span> ((iteration & <span class=number>0xf</span>) == <span class=number>0</span>) { <span class=comment>/* check once every 16 iterations. */</span></span><br><span class=line> elapsed = ustime()-start;</span><br><span class=line> <span class=keyword>if</span> (elapsed > timelimit) {</span><br><span class=line> timelimit_exit = <span class=number>1</span>;</span><br><span class=line> server.stat_expired_time_cap_reached_count++;</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 class=comment>/* We don't repeat the cycle for the current database if there are</span></span><br><span class=line><span class=comment> * an acceptable amount of stale keys (logically expired but yet</span></span><br><span class=line><span class=comment> * not reclained). */</span></span><br><span class=line> } <span class=keyword>while</span> ((expired*<span class=number>100</span>/sampled) > config_cycle_acceptable_stale);</span><br><span class=line> }</span><br><span class=line></span><br><span class=line> elapsed = ustime()-start;</span><br><span class=line> server.stat_expire_cycle_time_used += elapsed;</span><br><span class=line> latencyAddSampleIfNeeded(<span class=string>"expire-cycle"</span>,elapsed/<span class=number>1000</span>);</span><br><span class=line></span><br><span class=line> <span class=comment>/* Update our estimate of keys existing but yet to be expired.</span></span><br><span class=line><span class=comment> * Running average with this sample accounting for 5%. */</span></span><br><span class=line> <span class=type>double</span> current_perc;</span><br><span class=line> <span class=keyword>if</span> (total_sampled) {</span><br><span class=line> current_perc = (<span class=type>double</span>)total_expired/total_sampled;</span><br><span class=line> } <span class=keyword>else</span></span><br><span class=line> current_perc = <span class=number>0</span>;</span><br><span class=line> server.stat_expired_stale_perc = (current_perc*<span class=number>0.05</span>)+</span><br><span class=line> (server.stat_expired_stale_perc*<span class=number>0.95</span>);</span><br><span class=line>}</span><br></pre></table></figure><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<figure class="highlight c"><table><tr><td class=gutter><pre><span class=line>1</span><br><span class=line>2</span><br></pre><td class=code><pre><span class=line>onfig_cycle_fast_duration = ACTIVE_EXPIRE_CYCLE_FAST_DURATION +</span><br><span class=line> ACTIVE_EXPIRE_CYCLE_FAST_DURATION/<span class=number>4</span>*effort</span><br></pre></table></figure><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<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 class=code><pre><span class=line>config_keys_per_loop = ACTIVE_EXPIRE_CYCLE_KEYS_PER_LOOP +</span><br><span class=line> ACTIVE_EXPIRE_CYCLE_KEYS_PER_LOOP/<span class=number>4</span>*effort</span><br><span class=line>``` </span><br><span class=line>控制，慢速的执行时长是</span><br><span class=line>```C</span><br><span class=line>config_cycle_slow_time_perc = ACTIVE_EXPIRE_CYCLE_SLOW_TIME_PERC +</span><br><span class=line> <span class=number>2</span>*effort</span><br><span class=line>timelimit = config_cycle_slow_time_perc*<span class=number>1000000</span>/server.hz/<span class=number>100</span>;</span><br></pre></table></figure><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</div><footer class=post-footer><div class=reward-container><div>请我一杯咖啡吧！</div><button>赞赏</button><div class=post-reward><div><img alt="Nicksxs 微信" src=https://i.loli.net/2020/01/12/NUlWanT31E8LQGx.png><span>微信</span></div><div><img alt="Nicksxs 支付宝" src=https://ooo.0o0.ooo/2016/08/17/57b421e773057.jpg><span>支付宝</span></div></div></div><div class=post-copyright><ul><li class=post-copyright-author><strong>本文作者： </strong>Nicksxs<li class=post-copyright-link><strong>本文链接：</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 class=post-copyright-license><strong>版权声明： </strong>本博客所有文章除特别声明外，均采用 <a href=https://creativecommons.org/licenses/by-nc-sa/4.0/ rel=noopener target=_blank><i class="fab fa-fw 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