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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">19</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">28</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/ssh/" rel="tag">ssh</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%8B%E5%8A%A1/" rel="tag">事务</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">3</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">5</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 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href="/2021/08/15/redis-%E7%9A%84-rdb-%E5%92%8C-COW-%E4%BB%8B%E7%BB%8D/" class="post-title-link" itemprop="url">redis 的 rdb 和 COW 介绍</a></h2><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 title="创建时间:2021-08-15 21:22:05" itemprop="dateCreated datePublished" datetime="2021-08-15T21:22:05+08:00">2021-08-15</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><span id="/2021/08/15/redis-%E7%9A%84-rdb-%E5%92%8C-COW-%E4%BB%8B%E7%BB%8D/" class="post-meta-item leancloud_visitors" data-flag-title="redis 的 rdb 和 COW 介绍" 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"><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="/2021/08/15/redis-%E7%9A%84-rdb-%E5%92%8C-COW-%E4%BB%8B%E7%BB%8D/#disqus_thread" itemprop="discussionUrl"><span class="post-comments-count disqus-comment-count" data-disqus-identifier="2021/08/15/redis-的-rdb-和-COW-介绍/" itemprop="commentCount"></span></a></span></div></div></header><div class="post-body" itemprop="articleBody"><p>redis 在使用 rdb 策略进行备份时,rdb 的意思是会在开启备份的时候将开启时间点的内存数据进行备份,并且可以设置时间,这样子就是这个策略其实还是不完全可靠的,如果是在这个间隔中宕机了,或者间隔过长,不过这个不在这次的要说的内容中,如果自己去写这个 rdb 的策略可能就有点类似于 mvcc 的 redolog,需要知道这个时间点之前的数据是怎么样的,防止后面更改的干扰,但是这样一方面需要有比较复杂的 mvcc 实现,另一方面是很占用存储空间,所以 redis 在这里面使用了 COW (Copy On Write) 技术,这个技术呢以前听过,也大致了解是怎么个意思,这次稍微具体地来看下,其实 redis 的 copy-on-write 就是来自于 linux 的 cow</p><h3 id="Linux中的CopyOnWrite"><a href="#Linux中的CopyOnWrite" class="headerlink" title="Linux中的CopyOnWrite"></a>Linux中的CopyOnWrite</h3><p>fork()之后,kernel把父进程中所有的内存页的权限都设为read-only,然后子进程的地址空间指向父进程。当父子进程都只读内存时,相安无事。当其中某个进程写内存时,CPU硬件检测到内存页是read-only的,于是触发页异常中断(page-fault),陷入kernel的一个中断例程。中断例程中,kernel就会把触发的异常的页复制一份,于是父子进程各自持有独立的一份。这个操作其实可以类比为写屏障,正常的读取是没问题的,当有写入时就会分裂。</p><h3 id="CopyOnWrite的好处:"><a href="#CopyOnWrite的好处:" class="headerlink" title="CopyOnWrite的好处:"></a>CopyOnWrite的好处:</h3><p>1、减少分配和复制资源时带来的瞬时延迟;<br>2、减少不必要的资源分配;<br>CopyOnWrite的缺点:<br>1、如果父子进程都需要进行大量的写操作,会产生大量的分页错误(页异常中断page-fault);</p><h3 id="Redis中的CopyOnWrite"><a href="#Redis中的CopyOnWrite" class="headerlink" title="Redis中的CopyOnWrite"></a>Redis中的CopyOnWrite</h3><p>Redis在持久化时,如果是采用BGSAVE命令或者BGREWRITEAOF的方式,那Redis会fork出一个子进程来读取数据,从而写到磁盘中。<br>总体来看,Redis还是读操作比较多。如果子进程存在期间,发生了大量的写操作,那可能就会出现很多的分页错误(页异常中断page-fault),这样就得耗费不少性能在复制上。<br>而在rehash阶段上,写操作是无法避免的。所以Redis在fork出子进程之后,将负载因子阈值提高,尽量减少写操作,避免不必要的内存写入操作,最大限度地节约内存。这里其实更巧妙了,在细节上去优化会产生大量页异常中断的情况。</p></div><footer class="post-footer"><div class="post-eof"></div></footer></article></div><div class="post-block"><article itemscope itemtype="http://schema.org/Article" class="post-content"><link itemprop="mainEntityOfPage" href="https://nicksxs.me/2021/08/08/%E8%81%8A%E5%9C%A8%E4%B8%9C%E4%BA%AC%E5%A5%A5%E8%BF%90%E4%BC%9A%E9%97%AD%E5%B9%95%E5%BC%8F%E8%BF%99%E5%A4%A9/"><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"><h2 class="post-title" itemprop="name headline"><a href="/2021/08/08/%E8%81%8A%E5%9C%A8%E4%B8%9C%E4%BA%AC%E5%A5%A5%E8%BF%90%E4%BC%9A%E9%97%AD%E5%B9%95%E5%BC%8F%E8%BF%99%E5%A4%A9/" class="post-title-link" itemprop="url">聊在东京奥运会闭幕式这天</a></h2><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 title="创建时间:2021-08-08 20:05:07" itemprop="dateCreated datePublished" datetime="2021-08-08T20:05:07+08:00">2021-08-08</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/%E7%94%9F%E6%B4%BB/" itemprop="url" rel="index"><span itemprop="name">生活</span></a> </span>, <span itemprop="about" itemscope itemtype="http://schema.org/Thing"><a href="/categories/%E7%94%9F%E6%B4%BB/%E8%BF%90%E5%8A%A8/" itemprop="url" rel="index"><span itemprop="name">运动</span></a> </span></span><span id="/2021/08/08/%E8%81%8A%E5%9C%A8%E4%B8%9C%E4%BA%AC%E5%A5%A5%E8%BF%90%E4%BC%9A%E9%97%AD%E5%B9%95%E5%BC%8F%E8%BF%99%E5%A4%A9/" class="post-meta-item leancloud_visitors" data-flag-title="聊在东京奥运会闭幕式这天" 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"><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="/2021/08/08/%E8%81%8A%E5%9C%A8%E4%B8%9C%E4%BA%AC%E5%A5%A5%E8%BF%90%E4%BC%9A%E9%97%AD%E5%B9%95%E5%BC%8F%E8%BF%99%E5%A4%A9/#disqus_thread" itemprop="discussionUrl"><span class="post-comments-count disqus-comment-count" data-disqus-identifier="2021/08/08/聊在东京奥运会闭幕式这天/" itemprop="commentCount"></span></a></span></div></div></header><div class="post-body" itemprop="articleBody"><p>这届奥运会有可能是我除了 08 年之外关注度最高的一届奥运会,原因可能是因为最近也没什么电影综艺啥的比较好看,前面看跑男倒还行,不是说多好,也就图一乐,最开始看向往的生活觉得也挺不错的,后面变成了统一来了就看黄磊做饭,然后夸黄磊做饭好吃,然后无聊的说这种生活多么多么美好,单调无聊,差不多弃了,这里面还包括大华不在了,大华其实个人还是有点呱噪的,但是挺能搞气氛,并且也有才华,彭彭跟子枫人是不讨厌,但是撑不起来,所以也导致了前面说的结果,都变成了黄磊彩虹屁现场,虽然偶尔怀疑他是否做得好吃,但是整体还是承认的,可对于一个这么多季了的综艺来说,这样也有点单调了。</p><p>还有奥运会像乒乓球,篮球,跳水这几个都是比较喜欢的项目,篮球🏀是从初中开始就也有在自己在玩的,虽然因为身高啊体质基本没什么天赋,但也算是热爱驱动,差不多到了大学因为比较懒才放下了,初中高中还是有很多时间花在上面,不像别人经常打球跑跑跳跳还能长高,我反而一直都没长个子,也因为这个其实蛮遗憾的,后面想想可能是初中的时候远走他乡去住宿读初中,伙食营养跟不上导致的,可能也是自己的一厢情愿吧,总觉得应该还能再长点个,这一点以后我自己的小孩我应该会特别注意这段时间他/她的营养摄入了;然后像乒乓球🏓的话其实小时候是比较讨厌的,因为家里人,父母都没有这类爱好习惯,我也完全不会,但是小学那会班里的“恶霸”就以公平之名要我们男生每个人都排队打几个,我这种不会的反而又要被嘲笑,这个小时候的阴影让我有了比较不好的印象,对它🏓的改观是在工作以后,前司跟一个同样不会的同事经常在饭点会打打,而且那会因为这个其实身体得到了锻炼,感觉是个不错的健身方式,然后又是中国的优势项目,小时候跟着我爸看孔令辉,那时候完全不懂,印象就觉得老瓦很牛,后面其实也没那么关注,上一届好像看了马龙的比赛;跳水也是中国的优势项目,而且也比较简单,不是说真的很简单,就是我们外行观众看着就看看水花大小图一乐。</p><p>这次的观赛过程其实主要还是在乒乓球上面,现在都有点怪我的乌鸦嘴,混双我一直就不太放心(关我什么事,我也不专业),然后一直觉得混双是不是不太稳,结果那天看的时候也是因为央视一套跟五套都没放,我家的有线电视又是没有五加体育,然后用电脑投屏就很卡,看得也很不爽,同时那天因为看的时候已经是 2:0还是再后面点了,一方面是不懂每队只有一次暂停,另一方面不知道已经用过暂停了,所以就特别怀疑马林是不是只会无脑鼓掌,感觉作为教练,并且是前冠军,应该也能在擦汗间隙,或者局间休息调整的时候多给些战略战术的指导,类似于后面男团小胖打奥恰洛夫,像解说都看出来了,其实奥恰那会的反手特别顺,打得特别凶,那就不能让他能特别顺手的上反手位,这当然是外行比较粗浅的看法,在混双过程中其实除了这个,还有让人很不爽的就是我们的许昕跟刘诗雯有种拿不出破釜沉舟的勇气的感觉,在气势上完全被对面两位日本乒乓球最讨厌的两位对手压制着,我都要输了,我就每一颗都要不让你好过,因为真的不是说没有实力,对面水谷隼也不是多么多么强的,可能上一届男团许昕输给他还留着阴影,但是以许昕 19 年男单世界第一的实力,目前也排在世界前三,输一场不应该成为这种阻力,有一些失误也很可惜,后面孙颖莎真的打得很解气,第二局一度以为又要被翻盘了,结果来了个大逆转,女团的时候也是,感觉在心态上孙颖莎还是很值得肯定的,少年老成这个词很适合,看其他的视频也觉得莎莎萌萌哒,陈梦总感觉还欠一点王者霸气,王曼昱还是可以的,反手很凶,我觉得其实这一届日本女乒就是打得非常凶,即使像平野这种看着很弱的妹子,打的球可一点都不弱,也是这种凶狠的打法,有点要压制中国的感觉,这方面我觉得是需要改善的,打这种要不就是实力上的完全碾压,要不就是我实力虽然比较没强多少,但是你狠我打得比你还狠,越保守越要输,我不太成熟的想法是这样的,还有就是面对逆境,这个就要说到男队的了,樊振东跟马龙在半决赛的时候,特别是男团的第二盘,樊振东打奥恰很好地表现了这个心态,当然樊振东我不是特别了解,据说他是比较善于打相持,比较善于焦灼的情况,不过整体看下来樊振东还是有一些欠缺,就是面对情况的快速转变应对,这一点也是马龙特别强的,虽然看起来马龙真的是年纪大了点,没有 16 年那会满头发胶,油光锃亮的大背头和满脸胶原蛋白的意气风发,大范围运动能力也弱了一点,但是经验和能力的全面性也让他最终能再次站上巅峰,还是非常佩服的,这里提一下张继科,虽然可能天赋上是张继科更强点,但是男乒一直都是有强者出现,能为国家队付出这么多并且一直坚持的可不是人人都可以,即使现在同台竞技马龙打不过张继科我还是更喜欢马龙。再来说说我们的对手,主要分三部分,德国男乒,里面有波尔(我刚听到的时候在想怎么又出来个叫波尔的,是不是像举重的石智勇一样,又来一个同名的,结果是同一个,已经四十岁了),这真是个让人敬佩的对手,实力强,经验丰富,虽然男单有点可惜,但是帮助男团获得银牌,真的是起到了定海神针的作用;奥恰洛夫,以前完全不认识,或者说看过也忘了,这次是真的有点意外,竟然有这么个马龙护法,其实他也坦言非常想赢一次马龙,并且在半决赛也非常接近赢得比赛,是个实力非常强的对手,就是男团半决赛输给张本智和有点可惜,有点被打蒙的感觉,佛朗西斯卡的话也是实力不错的选手,就是可能被奥恰跟波尔的光芒掩盖了,跟波尔在男团第一盘男双的比赛中打败日本那对男双也是非常给力的,说实话,最后打国乒的时候的确是国乒实力更胜一筹,但是即使德国赢了我也是充满尊敬,拼的就是硬实力,就像第二盘奥恰打樊振东,反手是真的很强,反过来看奥恰可能也不是很善于快速调整,樊振东打出来自己的节奏,主攻奥恰的中路,他好像没什么好办法解决。再来说我最讨厌的日本,嗯,小日本,张本智和、水谷隼、伊藤美诚,一一评价下(我是外行,绝对主观评价),张本智和,父母也是中国人,原来叫张智和,改日本籍后加了个本,被微博网友笑称日本尖叫鸡,男单输给了斯洛文尼亚选手,男团里是赢了两场,但是在我看来其实实力上可能比不上全力的奥恰,主要是特别能叫,会干扰对手,如果觉得这种也是种能力我也无话可说,要是有那种吼声能直接把对手震聋的,都不需要打比赛了,我简单记了下,赢一颗球,他要叫八声,用 LD 的话来说烦都烦死了,心态是在面对一些困境顺境的应对调整适应能力,而不是对这种噪音的适应能力,至少我是这么看的,所以我很期待樊振东能好好地虐虐他,因为其他像林昀儒真的是非常优秀的新选手,所谓的国乒克星估计也是小日本自己说说的,国乒其实有很多对手,马龙跟樊振东在男单半决赛碰到的这两个几乎都差点把他们掀翻了,所以还是练好自己的实力再来吹吧,免得打脸;水谷隼的话真的是长相就是特别地讨厌,还搞出那套不打比赛的姿态,男团里被波尔干掉就是很好的例子,波尔虽然真的很强,但毕竟 40 岁了,跟伊藤美诚一起说了吧,伊藤实力说实话是有的,混双中很大一部分的赢面来自于她,刘诗雯做了手术状态不好,许昕失误稍多,但是这种赢球了就感觉我赢了你一辈子一场没输的感觉,还有那种不知道怎么形容的笑,实力强的正常打比赛的我都佩服,像女团决赛里,平野跟石川佳纯的打法其实也很凶狠,但是都是正常的比赛,即使中国队两位实力不济输了也很正常,这种就真的需要像孙颖莎这样的小魔王无视各种魔法攻击,无视你各种花里胡哨的打法的人好好教训一下,混双输了以后了解了下她,感觉实力真的不错,是个大威胁,但是其实我们孙颖莎也是经历了九个月的继续成长,像张怡宁也评价了她,可能后面就没什么空间了,当然如果由张怡宁来打她就更适合了,净整这些有的没的,就打得你没脾气。</p><p>乒乓球的说的有点多,就分篇说了,第一篇先到这。</p></div><footer class="post-footer"><div class="post-eof"></div></footer></article></div><div class="post-block"><article itemscope itemtype="http://schema.org/Article" class="post-content"><link itemprop="mainEntityOfPage" href="https://nicksxs.me/2021/08/01/redis%E6%B7%98%E6%B1%B0%E7%AD%96%E7%95%A5%E5%A4%8D%E4%B9%A0/"><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"><h2 class="post-title" itemprop="name headline"><a href="/2021/08/01/redis%E6%B7%98%E6%B1%B0%E7%AD%96%E7%95%A5%E5%A4%8D%E4%B9%A0/" class="post-title-link" itemprop="url">redis淘汰策略复习</a></h2><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 title="创建时间:2021-08-01 20:19:53" itemprop="dateCreated datePublished" datetime="2021-08-01T20:19:53+08:00">2021-08-01</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><span id="/2021/08/01/redis%E6%B7%98%E6%B1%B0%E7%AD%96%E7%95%A5%E5%A4%8D%E4%B9%A0/" class="post-meta-item leancloud_visitors" data-flag-title="redis淘汰策略复习" 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"><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="/2021/08/01/redis%E6%B7%98%E6%B1%B0%E7%AD%96%E7%95%A5%E5%A4%8D%E4%B9%A0/#disqus_thread" itemprop="discussionUrl"><span class="post-comments-count disqus-comment-count" data-disqus-identifier="2021/08/01/redis淘汰策略复习/" itemprop="commentCount"></span></a></span></div></div></header><div class="post-body" itemprop="articleBody"><p>前面复习了 redis 的过期策略,这里再复习下淘汰策略,淘汰跟过期的区别有时候会被混淆了,过期主要针对那些设置了过期时间的 key,应该说是一种逻辑策略,是主动的还是被动的加定时的,两种有各自的取舍,而淘汰也可以看成是一种保持系统稳定的策略,因为如果内存满了,不采取任何策略处理,那大概率会导致系统故障,之前其实主要从源码角度分析过redis 的 LRU 和 LFU,但这个是偏底层的实现,抠得比较细,那么具体的系统层面的配置是有哪些策略,来看下 redis labs 的介绍</p><table><thead><tr><th align="center"><strong>Policy</strong></th><th align="center"><strong>Description</strong></th></tr></thead><tbody><tr><td align="center">noeviction 不逐出</td><td align="center">Returns an error if the memory limit has been reached when trying to insert more data,插入更多数据时,如果内存达到上限了,返回错误</td></tr><tr><td align="center">allkeys-lru 所有的 key 使用 lru 逐出</td><td align="center">Evicts the least recently used keys out of all keys 在所有 key 中逐出最近最少使用的</td></tr><tr><td align="center">allkeys-lfu 所有的 key 使用 lfu 逐出</td><td align="center">Evicts the least frequently used keys out of all keys 在所有 key 中逐出最近最不频繁使用的</td></tr><tr><td align="center">allkeys-random 所有的 key 中随机逐出</td><td align="center">Randomly evicts keys out of all keys 在所有 key 中随机逐出</td></tr><tr><td align="center">volatile-lru</td><td align="center">Evicts the least recently used keys out of all keys with an “expire” field set 在设置了过期时间的 key 空间 expire 中使用 lru 策略逐出</td></tr><tr><td align="center">volatile-lfu</td><td align="center">Evicts the least frequently used keys out of all keys with an “expire” field set 在设置了过期时间的 key 空间 expire 中使用 lfu 策略逐出</td></tr><tr><td align="center">volatile-random</td><td align="center">Randomly evicts keys with an “expire” field set 在设置了过期时间的 key 空间 expire 中随机逐出</td></tr><tr><td align="center">volatile-ttl</td><td align="center">Evicts the shortest time-to-live keys out of all keys with an “expire” field set.在设置了过期时间的 key 空间 expire 中逐出更早过期的</td></tr></tbody></table><p>而在这其中默认使用的策略是 volatile-lru,对 lru 跟 lfu 想有更多的了解可以看下我之前的文章<a href="https://nicksxs.me/2020/04/18/redis%E7%B3%BB%E5%88%97%E4%BB%8B%E7%BB%8D%E5%85%AB/">redis系列介绍八-淘汰策略</a></p></div><footer class="post-footer"><div class="post-eof"></div></footer></article></div><div class="post-block"><article itemscope itemtype="http://schema.org/Article" class="post-content"><link itemprop="mainEntityOfPage" href="https://nicksxs.me/2021/07/25/redis%E8%BF%87%E6%9C%9F%E7%AD%96%E7%95%A5%E5%A4%8D%E4%B9%A0/"><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"><h2 class="post-title" itemprop="name headline"><a href="/2021/07/25/redis%E8%BF%87%E6%9C%9F%E7%AD%96%E7%95%A5%E5%A4%8D%E4%B9%A0/" class="post-title-link" itemprop="url">redis过期策略复习</a></h2><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 title="创建时间:2021-07-25 21:28:23" itemprop="dateCreated datePublished" datetime="2021-07-25T21:28:23+08:00">2021-07-25</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><span id="/2021/07/25/redis%E8%BF%87%E6%9C%9F%E7%AD%96%E7%95%A5%E5%A4%8D%E4%B9%A0/" class="post-meta-item leancloud_visitors" data-flag-title="redis过期策略复习" 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"><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="/2021/07/25/redis%E8%BF%87%E6%9C%9F%E7%AD%96%E7%95%A5%E5%A4%8D%E4%B9%A0/#disqus_thread" itemprop="discussionUrl"><span class="post-comments-count disqus-comment-count" data-disqus-identifier="2021/07/25/redis过期策略复习/" itemprop="commentCount"></span></a></span></div></div></header><div class="post-body" itemprop="articleBody"><h1 id="redis过期策略复习"><a href="#redis过期策略复习" class="headerlink" title="redis过期策略复习"></a>redis过期策略复习</h1><p>之前其实写过redis的过期的一些原理,这次主要是记录下,一些使用上的概念,主要是redis使用的过期策略是懒过期和定时清除,懒过期的其实比较简单,即是在key被访问的时候会顺带着判断下这个key是否已过期了,如果已经过期了,就不返回了,但是这种策略有个漏洞是如果有些key之后一直不会被访问了,就等于沉在池底了,所以需要有一个定时的清理机制,去从设置了过期的key池子(expires)里随机地捞key,具体的策略我们看下官网的解释</p><ol><li>Test 20 random keys from the set of keys with an associated expire.</li><li>Delete all the keys found expired.</li><li>If more than 25% of keys were expired, start again from step 1.</li></ol><p>从池子里随机获取20个key,将其中过期的key删掉,如果这其中有超过25%的key已经过期了,那就再来一次,以此保持过期的key不超过25%(左右),并且这个定时策略可以在redis的配置文件</p><pre class="line-numbers language-shell" data-language="shell"><code class="language-shell"># Redis calls an internal function to perform many background tasks, like
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