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<!DOCTYPE html>
<html>
<head>
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<meta name="renderer" content="webkit">
<meta http-equiv="X-UA-Compatible" content="IE=edge" >
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background: linear-gradient(200deg,#a0cfe4,#e8c37e);
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<a href="/" class="profilepic">
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<nav class="header-nav">
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<a class="github" target="_blank" href="https://github.com/dejavu-git" title="github"><i class="icon-github"></i></a>
<a class="qq" target="_blank" href="/img/qq.jpg" title="qq"><i class="icon-qq"></i></a>
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</div>
</nav>
<nav class="header-menu js-header-menu">
<ul style="width: 70%">
<li style="width: 33.333333333333336%"><a href="/">主页</a></li>
<li style="width: 33.333333333333336%"><a href="/tags/%E9%9A%8F%E7%AC%94/">随笔</a></li>
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</ul>
</nav>
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</nav>
<div id="wrapper" class="body-wrap">
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</div>
<div id="js-content" class="content-ll">
<article id="post-redis之缓存击穿" class="article article-type-post article-index" itemscope itemprop="blogPost">
<div class="article-inner">
<header class="article-header">
<h1 itemprop="name">
<a class="article-title" href="/2023/02/11/redis%E4%B9%8B%E7%BC%93%E5%AD%98%E5%87%BB%E7%A9%BF/">redis之缓存击穿</a>
</h1>
<a href="/2023/02/11/redis%E4%B9%8B%E7%BC%93%E5%AD%98%E5%87%BB%E7%A9%BF/" class="archive-article-date">
<time datetime="2023-02-11T09:39:12.000Z" itemprop="datePublished"><i class="icon-calendar icon"></i>2023-02-11</time>
</a>
</header>
<div class="article-entry" itemprop="articleBody">
<p>缓存击穿问题也叫热点key问题，就是一个被高并发访问并且缓存重建业务较复杂的key突然失效了，无数的请求访问会在瞬间给数据库带来巨大的冲击。<br>解决方案：</p>
<ul>
<li>互斥锁<ul>
<li>优点：<ul>
<li>没有额外的内存消耗</li>
<li>保证一致性</li>
<li>实现简单</li>
</ul>
</li>
<li>缺点：<ul>
<li>线程需要等待，性能受影响</li>
<li>可能有死锁风险</li>
</ul>
</li>
</ul>
</li>
<li>逻辑过期<ul>
<li>优点：<ul>
<li>线程无需等待，性能较好</li>
</ul>
</li>
<li>缺点：<ul>
<li>不保证一致性</li>
<li>有额外内存消耗</li>
<li>实现复杂</li>
</ul>
</li>
</ul>
</li>
</ul>
</div>
<div class="article-info article-info-index">
<div class="article-tag tagcloud">
<i class="icon-price-tags icon"></i>
<ul class="article-tag-list">
<li class="article-tag-list-item">
<a href="javascript:void(0)" class="js-tag article-tag-list-link color5">学习笔记</a>
</li>
<li class="article-tag-list-item">
<a href="javascript:void(0)" class="js-tag article-tag-list-link color1">redis</a>
</li>
</ul>
</div>
<p class="article-more-link">
<a class="article-more-a" href="/2023/02/11/redis%E4%B9%8B%E7%BC%93%E5%AD%98%E5%87%BB%E7%A9%BF/">展开全文 >></a>
</p>
<div class="clearfix"></div>
</div>
</div>
</article>
<aside class="wrap-side-operation">
<div class="mod-side-operation">
<div class="jump-container" id="js-jump-container" style="display:none;">
<a href="javascript:void(0)" class="mod-side-operation__jump-to-top">
<i class="icon-font icon-back"></i>
</a>
<div id="js-jump-plan-container" class="jump-plan-container" style="top: -11px;">
<i class="icon-font icon-plane jump-plane"></i>
</div>
</div>
</div>
</aside>
<article id="post-redis之缓存雪崩" class="article article-type-post article-index" itemscope itemprop="blogPost">
<div class="article-inner">
<header class="article-header">
<h1 itemprop="name">
<a class="article-title" href="/2023/02/11/redis%E4%B9%8B%E7%BC%93%E5%AD%98%E9%9B%AA%E5%B4%A9/">redis之缓存雪崩</a>
</h1>
<a href="/2023/02/11/redis%E4%B9%8B%E7%BC%93%E5%AD%98%E9%9B%AA%E5%B4%A9/" class="archive-article-date">
<time datetime="2023-02-11T09:32:51.000Z" itemprop="datePublished"><i class="icon-calendar icon"></i>2023-02-11</time>
</a>
</header>
<div class="article-entry" itemprop="articleBody">
<p>缓存雪崩是指在同一时段大量的缓存key同时失效或redis服务器宕机，导致大量的请求到达数据库，带来巨大压力。<br>解决方案：</p>
<ul>
<li>给不同的key的TTL添加随机值</li>
<li>利用redis集群提高服务的可用性</li>
<li>给缓存业务添加降级限流策略</li>
<li>给业务添加多级缓存</li>
</ul>
</div>
<div class="article-info article-info-index">
<div class="article-tag tagcloud">
<i class="icon-price-tags icon"></i>
<ul class="article-tag-list">
<li class="article-tag-list-item">
<a href="javascript:void(0)" class="js-tag article-tag-list-link color5">学习笔记</a>
</li>
<li class="article-tag-list-item">
<a href="javascript:void(0)" class="js-tag article-tag-list-link color1">redis</a>
</li>
</ul>
</div>
<p class="article-more-link">
<a class="article-more-a" href="/2023/02/11/redis%E4%B9%8B%E7%BC%93%E5%AD%98%E9%9B%AA%E5%B4%A9/">展开全文 >></a>
</p>
<div class="clearfix"></div>
</div>
</div>
</article>
<aside class="wrap-side-operation">
<div class="mod-side-operation">
<div class="jump-container" id="js-jump-container" style="display:none;">
<a href="javascript:void(0)" class="mod-side-operation__jump-to-top">
<i class="icon-font icon-back"></i>
</a>
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<i class="icon-font icon-plane jump-plane"></i>
</div>
</div>
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</aside>
<article id="post-redis之缓存穿透" class="article article-type-post article-index" itemscope itemprop="blogPost">
<div class="article-inner">
<header class="article-header">
<h1 itemprop="name">
<a class="article-title" href="/2023/02/11/redis%E4%B9%8B%E7%BC%93%E5%AD%98%E7%A9%BF%E9%80%8F/">redis之缓存穿透</a>
</h1>
<a href="/2023/02/11/redis%E4%B9%8B%E7%BC%93%E5%AD%98%E7%A9%BF%E9%80%8F/" class="archive-article-date">
<time datetime="2023-02-11T08:50:15.000Z" itemprop="datePublished"><i class="icon-calendar icon"></i>2023-02-11</time>
</a>
</header>
<div class="article-entry" itemprop="articleBody">
<p>缓存穿透是指客户端请求的数据在缓存中和数据库中都不存在，这样缓存永远不会生效，这些请求都会打到数据库。<br>解决方案：</p>
<ul>
<li>缓存空对象<ul>
<li>优点：实现简单，维护方便</li>
<li>缺点：<ul>
<li>额外的内存消耗</li>
<li>可能造成短期的不一致</li>
</ul>
</li>
</ul>
</li>
<li>布隆过滤<ul>
<li>优点：内存占用少，没有多余的KEY</li>
<li>缺点：<ul>
<li>实现复杂</li>
<li>存在误判可能</li>
</ul>
</li>
</ul>
</li>
</ul>
</div>
<div class="article-info article-info-index">
<div class="article-tag tagcloud">
<i class="icon-price-tags icon"></i>
<ul class="article-tag-list">
<li class="article-tag-list-item">
<a href="javascript:void(0)" class="js-tag article-tag-list-link color5">学习笔记</a>
</li>
<li class="article-tag-list-item">
<a href="javascript:void(0)" class="js-tag article-tag-list-link color1">redis</a>
</li>
</ul>
</div>
<p class="article-more-link">
<a class="article-more-a" href="/2023/02/11/redis%E4%B9%8B%E7%BC%93%E5%AD%98%E7%A9%BF%E9%80%8F/">展开全文 >></a>
</p>
<div class="clearfix"></div>
</div>
</div>
</article>
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<article id="post-序列化与反序列化" class="article article-type-post article-index" itemscope itemprop="blogPost">
<div class="article-inner">
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<a class="article-title" href="/2023/02/03/%E5%BA%8F%E5%88%97%E5%8C%96%E4%B8%8E%E5%8F%8D%E5%BA%8F%E5%88%97%E5%8C%96/">序列化与反序列化</a>
</h1>
<a href="/2023/02/03/%E5%BA%8F%E5%88%97%E5%8C%96%E4%B8%8E%E5%8F%8D%E5%BA%8F%E5%88%97%E5%8C%96/" class="archive-article-date">
<time datetime="2023-02-03T12:12:00.000Z" itemprop="datePublished"><i class="icon-calendar icon"></i>2023-02-03</time>
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<li>序列化与反序列化<ul>
<li>序列化就是在保存数据时，保存数据的值和数据类型</li>
<li>反序列化就是在恢复数据时，恢复数据的值和数据类型</li>
<li>需要让某个对象支持序列化机制，则必须让其类是可序列化的，该类必须实现如下两个接口之一：<ul>
<li>Serializable //标记接口，没有方法，主要使用该接口</li>
<li>Externalizable //该接口有方法需要实现</li>
</ul>
</li>
<li>读写顺序要一致</li>
<li>序列化的类中建议添加SerialVersionUID，为了提高版本的兼容性 //private static final long serialVersionUID = 1L;</li>
<li>序列化对象时，默认将里面的所有属性进行序列化，除了static或transient修饰的成员</li>
<li>序列化对象时，要求里面属性的类型也需要实现序列化接口</li>
<li>序列化具备可继承性</li>
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<a href="/2023/01/22/%E6%80%BB%E7%BB%93%EF%BC%9A%E5%BC%80%E5%8F%91%E4%B8%AD%E5%A6%82%E4%BD%95%E9%80%89%E6%8B%A9%E9%9B%86%E5%90%88%E5%AE%9E%E7%8E%B0%E7%B1%BB/" class="archive-article-date">
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<li>先判断存储的类型（一组对象[单列]或一组键值对[单列]）</li>
<li>一组对象（单列）：Collection接口<ul>
<li>允许重复：List<ul>
<li>增删多：LinkedList（底层维护了一个双向链表）</li>
<li>改查多：ArrayList（底层维护了一个Obiect类型的可变数组）</li>
</ul>
</li>
<li>不允许重复：Set<ul>
<li>无序：HashSet（底层是HashMap，维护了一个哈希表（数组+链表+红黑树））</li>
<li>排序：TreeSet</li>
<li>插入和取出顺序一致：LinkedHashSet（底层维护了一个数组+双向链表）</li>
</ul>
</li>
</ul>
</li>
<li>一组键值对（双列）：Map<ul>
<li>键无序：HashMap（数组+链表+红黑树）</li>
<li>键排序：TreeMap</li>
<li>键插入顺序和取出顺序一致：LinkedHashMap</li>
<li>读取文件：Properties</li>
</ul>
</li>
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<a class="article-title" href="/2023/01/15/Set%E6%8E%A5%E5%8F%A3%E5%8F%8A%E5%85%B6%E5%AE%9E%E7%8E%B0%E7%B1%BB/">Set接口及其实现类</a>
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<a href="/2023/01/15/Set%E6%8E%A5%E5%8F%A3%E5%8F%8A%E5%85%B6%E5%AE%9E%E7%8E%B0%E7%B1%BB/" class="archive-article-date">
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<h3 id="Set接口基本介绍"><a href="#Set接口基本介绍" class="headerlink" title="Set接口基本介绍"></a>Set接口基本介绍</h3><ol>
<li>无序，没有索引</li>
<li>不允许重复元素，最多包含一个null</li>
</ol>
<h3 id="Set接口实现类-HashSet"><a href="#Set接口实现类-HashSet" class="headerlink" title="Set接口实现类 HashSet"></a>Set接口实现类 HashSet</h3><ol>
<li>HashSet 实现Set接口</li>
<li>HashSet 实际上是 HashMap</li>
<li>只能存放一个null值</li>
<li>不保证元素有序，取决于hash后，在确定索引的结果（即不保证存放元素的顺序和取出的顺序是一样的）</li>
<li>不能有重复的对象/元素</li>
</ol>
<h3 id="HashSet底层机制说明"><a href="#HashSet底层机制说明" class="headerlink" title="HashSet底层机制说明"></a>HashSet底层机制说明</h3><ol>
<li>HashSet底层是HashMap</li>
<li>添加一个元素时，先得到hash值，再转化成索引值</li>
<li>找到存储数据表table，看这个索引位置是否已经存放元素。若没有，则直接加入；若有，则调用equal比较，如果相同，则放弃添加，如果不同，则添加到最后</li>
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<a href="/2023/01/15/Vector%E5%BA%95%E5%B1%82%E7%BB%93%E6%9E%84%E5%92%8CArrayList%E7%9A%84%E6%AF%94%E8%BE%83/" class="archive-article-date">
<time datetime="2023-01-15T10:39:59.000Z" itemprop="datePublished"><i class="icon-calendar icon"></i>2023-01-15</time>
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<h2 id="Vector-和-ArrayList的比较"><a href="#Vector-和-ArrayList的比较" class="headerlink" title="Vector 和 ArrayList的比较"></a>Vector 和 ArrayList的比较</h2><table>
<thead>
<tr>
<th align="center">数据结构</th>
<th align="center">底层结构</th>
<th align="center">线程安全</th>
<th align="center">扩容倍数</th>
</tr>
</thead>
<tbody><tr>
<td align="center">ArrayList</td>
<td align="center">可变数组</td>
<td align="center">不安全，效率高</td>
<td align="center">1.5倍</td>
</tr>
<tr>
<td align="center">Vector</td>
<td align="center">可变数组</td>
<td align="center">安全，效率不高</td>
<td align="center">2倍</td>
</tr>
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<article id="post-ArrayList底层源码和扩容机制" class="article article-type-post article-index" itemscope itemprop="blogPost">
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<a class="article-title" href="/2023/01/14/ArrayList%E5%BA%95%E5%B1%82%E6%BA%90%E7%A0%81%E5%92%8C%E6%89%A9%E5%AE%B9%E6%9C%BA%E5%88%B6/">ArrayList底层源码和扩容机制</a>
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<p> 1.ArrayList中维护了一个Object类型的数组 transient Object[] elementData; // transient表示该属性不会被序列化</p>
<p> 2.当创建ArrayList对象时，若使用的是无参构造器，则初始elementData容量为0时，第一次添加，则扩容的大小为10，后续若再次扩容，则扩容elementData为1.5倍。扩容使用的是Arrays.copyOf()<br> //源码：grow函数 int newCapacity = oldCapacity + (oldCapacity >> 1); </p>
<p> 3.若使用的是指定大小的构造器，则初始容量为指定大小，后续若再次扩容，则扩容elementData为1.5倍。</p>
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<article id="post-剑指-Offer-26-树的子结构" class="article article-type-post article-index" itemscope itemprop="blogPost">
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<a class="article-title" href="/2023/01/12/%E5%89%91%E6%8C%87-Offer-26-%E6%A0%91%E7%9A%84%E5%AD%90%E7%BB%93%E6%9E%84/">剑指 Offer 26. 树的子结构</a>
</h1>
<a href="/2023/01/12/%E5%89%91%E6%8C%87-Offer-26-%E6%A0%91%E7%9A%84%E5%AD%90%E7%BB%93%E6%9E%84/" class="archive-article-date">
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<p>链接附上</p>
<h3 id="剑指-Offer-26-树的子结构"><a href="#剑指-Offer-26-树的子结构" class="headerlink" title="剑指 Offer 26. 树的子结构"></a><a target="_blank" rel="noopener" href="https://leetcode.cn/problems/shu-de-zi-jie-gou-lcof/">剑指 Offer 26. 树的子结构</a></h3><p><img src="https://note.youdao.com/yws/res/4/WEBRESOURCE8de4e24da1b985a05b13cc063f1c7caf" alt="题目"></p>
<p>评论里看到的代码，好优美简洁，再看看自己写的简直是依托答辩 TAT<br>希望自己以后也能独自写出这么优美的代码。</p>
<h3 id="思路"><a href="#思路" class="headerlink" title="思路"></a>思路</h3><ol>
<li>先用先序遍历找到A中B的相等节点</li>
<li>再以这个节点为根节点开始判断两个树结构是否相等</li>
<li>如果结构不相等再继续寻找下一个相等节点</li>
</ol>
<h3 id="题解"><a href="#题解" class="headerlink" title="题解"></a>题解</h3><figure class="highlight java"><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></pre></td><td class="code"><pre><span class="line"><span class="keyword">class</span> <span class="title class_">Solution</span> {</span><br><span class="line"> <span class="keyword">public</span> <span class="type">boolean</span> <span class="title function_">isSubStructure</span><span class="params">(TreeNode A, TreeNode B)</span> {</span><br><span class="line"> <span class="keyword">if</span>(A == <span class="literal">null</span> || B == <span class="literal">null</span>) <span class="keyword">return</span> <span class="literal">false</span>;</span><br><span class="line"> <span class="comment">//此处递归是为了找root一致的节点</span></span><br><span class="line"> <span class="keyword">return</span> dfs(A, B) || isSubStructure(A.left, B) || isSubStructure(A.right, B);</span><br><span class="line"> }</span><br><span class="line"> <span class="comment">//深度遍历，判断结构是否一致</span></span><br><span class="line"> <span class="type">boolean</span> <span class="title function_">dfs</span><span class="params">(TreeNode A, TreeNode B)</span>{</span><br><span class="line"> <span class="keyword">if</span>(B == <span class="literal">null</span>) <span class="keyword">return</span> <span class="literal">true</span>;</span><br><span class="line"> <span class="keyword">if</span>(A == <span class="literal">null</span>) <span class="keyword">return</span> <span class="literal">false</span>;</span><br><span class="line"> <span class="keyword">return</span> A.val == B.val && dfs(A.left, B.left) && dfs(A.right, B.right);</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
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<a class="article-title" href="/2023/01/10/hello-world/">Hello World</a>
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<p>Welcome to <a target="_blank" rel="noopener" href="https://hexo.io/">Hexo</a>! This is your very first post. Check <a target="_blank" rel="noopener" href="https://hexo.io/docs/">documentation</a> for more info. If you get any problems when using Hexo, you can find the answer in <a target="_blank" rel="noopener" href="https://hexo.io/docs/troubleshooting.html">troubleshooting</a> or you can ask me on <a target="_blank" rel="noopener" href="https://github.com/hexojs/hexo/issues">GitHub</a>.</p>
<h2 id="Quick-Start"><a href="#Quick-Start" class="headerlink" title="Quick Start"></a>Quick Start</h2><h3 id="Create-a-new-post"><a href="#Create-a-new-post" class="headerlink" title="Create a new post"></a>Create a new post</h3><figure class="highlight bash"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">$ hexo new <span class="string">"My New Post"</span></span><br></pre></td></tr></table></figure>