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<!DOCTYPE html><html lang="zh-CN" data-theme="light"><head><meta charset="UTF-8"><meta http-equiv="X-UA-Compatible" content="IE=edge"><meta name="viewport" content="width=device-width,initial-scale=1"><title>混饭's Notes - Quick notes</title><meta name="description" content="重度拖延症患者(-__-)b"><meta name="author" content="混饭"><meta name="copyright" content="混饭"><meta name="format-detection" content="telephone=no"><link rel="shortcut icon" href="/images/avatar.png"><link rel="canonical" href="https://hunfan.top/"><meta http-equiv="Cache-Control" content="no-transform"><meta http-equiv="Cache-Control" content="no-siteapp"><link rel="preconnect" href="//cdn.jsdelivr.net"/><link rel="preconnect" href="//hm.baidu.com"/><link rel="preconnect" href="//fonts.googleapis.com" crossorigin="crossorigin"/><link rel="preconnect" href="//busuanzi.ibruce.info"/><link rel="preconnect" href="//zz.bdstatic.com"/><meta property="og:type" content="website"><meta property="og:title" content="混饭's Notes"><meta property="og:url" content="https://hunfan.top/"><meta property="og:site_name" content="混饭's Notes"><meta property="og:description" content="重度拖延症患者(-__-)b"><meta property="og:image" content="https://hunfan.top/images/avatar.png"><meta property="article:published_time" content="2022-04-13T09:49:07.141Z"><meta property="article:modified_time" content="2022-04-13T09:49:07.141Z"><meta name="twitter:card" content="summary"><script>var activateDarkMode = function () {
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根据圆心、半径计算圆上点集的算法首先来分析一下，这个问题可以转换成数学上的平面坐标系计算，已知圆心坐标(x0,y0)，半径r，角度a0，求圆上任一点公式为：
x1 = x0 + r * cos(a0 * π/180)y1 = y0 + r * sin(a0 * π/180)
其中a0 * π/180(角度乘以π/180)，目的是将角度a0转换为弧度。
下面将平面上的圆等分为6份(如下图)，根据公式代入圆心坐标、弧度和半径计算出对应圆弧半径与圆交点的平面坐标。
这样就获得了6个平面圆上的坐标点，(x1,y1)、(x2,y2)…(x6,y6)，注意此时的点只是数学意义上的点，接下来需要将平面的点投影到地图上，获取地图经纬度的点集。
将平面坐标投影到地图在介绍如何将平面坐标投影到地图之前，我们首先需要了解一个概念:墨卡托投影。
众所周知，地球是一个不规则的球体，而我们平时看到的地图大多是平面的，那么如何将一个三维的地球画到平面上的呢。
墨卡托投影就是将三维的地球表示在一个二维平面上的方法之一，也是应用得最 ...</div></div></div><div class="recent-post-item"><div class="post_cover right_radius"><a href="/posts/ecdd7de8/" title="Google,Twitter和Spotify怎样建立文档文化"> <img class="post_bg" data-src="/upload/homePage/20181105161104.jpg" onerror="this.onerror=null;this.src='/img/404.jpg'" alt="Google,Twitter和Spotify怎样建立文档文化"></a></div><div class="recent-post-info"><a class="article-title" href="/posts/ecdd7de8/" title="Google,Twitter和Spotify怎样建立文档文化">Google,Twitter和Spotify怎样建立文档文化</a><div class="article-meta-wrap"><time class="post-meta__date"><span class="post-meta__date-created" title="发表于 2021-11-08 09:20:34"><i class="far fa-calendar-alt"></i>2021-11-08</span><span class="article-meta__separator">|</span><span class="post-meta__date-updated" title="更新于 2022-04-13 16:41:29"><i class="fas fa-history"></i>2022-04-13</span></time><span class="article-meta"><span class="article-meta__separator">|</span><i class="fas fa-inbox article-meta__icon"></i><a class="article-meta__categories" href="/categories/uncategorized/">uncategorized</a></span><span class="article-meta tags"><span class="article-meta__separator">|</span><i class="fas fa-tag article-meta__icon"></i><a class="article-meta__tags" href="/tags/google/">google</a><span class="article-meta__link">•</span><a class="article-meta__tags" href="/tags/twitter/">twitter</a><span class="article-meta__link">•</span><a class="article-meta__tags" href="/tags/spotify/">spotify</a><span class="article-meta__link">•</span><a class="article-meta__tags" href="/tags/docs/">docs</a></span></div><div class="content">许多技术问题
[原文链接]https://blog.doctave.com/2021/09/07/how-google-twitter-and-spotify-build-culture-of-documentation.html
</div></div></div><div class="recent-post-item"><div class="post_cover left_radius"><a href="/posts/204726e2/" title="Spring声明式事务Transactional原理只看这一篇就够了"> <img class="post_bg" data-src="/upload/homePage/20210928152000.jpg" onerror="this.onerror=null;this.src='/img/404.jpg'" alt="Spring声明式事务Transactional原理只看这一篇就够了"></a></div><div class="recent-post-info"><a class="article-title" href="/posts/204726e2/" title="Spring声明式事务Transactional原理只看这一篇就够了">Spring声明式事务Transactional原理只看这一篇就够了</a><div class="article-meta-wrap"><time class="post-meta__date"><span class="post-meta__date-created" title="发表于 2021-09-28 15:18:34"><i class="far fa-calendar-alt"></i>2021-09-28</span><span class="article-meta__separator">|</span><span class="post-meta__date-updated" title="更新于 2021-09-29 17:14:07"><i class="fas fa-history"></i>2021-09-29</span></time><span class="article-meta"><span class="article-meta__separator">|</span><i class="fas fa-inbox article-meta__icon"></i><a class="article-meta__categories" href="/categories/uncategorized/">uncategorized</a></span><span class="article-meta tags"><span class="article-meta__separator">|</span><i class="fas fa-tag article-meta__icon"></i><a class="article-meta__tags" href="/tags/spring/">spring</a><span class="article-meta__link">•</span><a class="article-meta__tags" href="/tags/transaction/">transaction</a></span></div><div class="content">问题Spring声明式事务@Transactional在同一个类中的两个方法之间调用失效是个老生常谈的问题，之前恰巧又遇到有这么写的同学，今天就翻一翻源码，总结一下其背后的原因。
初步分析由于Spring声明式事务采用动态代理（AOP）实现，它会在代码运行时为类生成一个代理对象，实际会使用代理对象调用业务方法，并在方法调用之前决定是否开启一个事务，在方法执行之后决定事务的提交和回滚。
其相当于下面这段代码：
// 业务方法 main { bizMethod();}// 经过AOP事务增强后main { Connection con = null; try{ con = getConnection(); con.setAutoCommit(false); //方法调用 bizMethod(); //提交事务 con.commit(); } catch(Run ...</div></div></div><div class="recent-post-item"><div class="post_cover right_radius"><a href="/posts/6a76cba2/" title="Nodejs14大版本特性以及版本管理n模块"> <img class="post_bg" data-src="/upload/homePage/20210517184300.jpg" onerror="this.onerror=null;this.src='/img/404.jpg'" alt="Nodejs14大版本特性以及版本管理n模块"></a></div><div class="recent-post-info"><a class="article-title" href="/posts/6a76cba2/" title="Nodejs14大版本特性以及版本管理n模块">Nodejs14大版本特性以及版本管理n模块</a><div class="article-meta-wrap"><time class="post-meta__date"><span class="post-meta__date-created" title="发表于 2021-04-26 14:43:09"><i class="far fa-calendar-alt"></i>2021-04-26</span><span class="article-meta__separator">|</span><span class="post-meta__date-updated" title="更新于 2021-05-17 18:46:43"><i class="fas fa-history"></i>2021-05-17</span></time><span class="article-meta"><span class="article-meta__separator">|</span><i class="fas fa-inbox article-meta__icon"></i><a class="article-meta__categories" href="/categories/uncategorized/">uncategorized</a></span><span class="article-meta tags"><span class="article-meta__separator">|</span><i class="fas fa-tag article-meta__icon"></i><a class="article-meta__tags" href="/tags/nodejs/">nodejs</a></span></div><div class="content">情景前段时间在Github看到有这么一种写法：
data = $request(params)if (data?.data?.bizCode === 0) { console.log(`任务完成成功，获得：${data?.data?.result?.produceScore ?? "未知"}能量`);}
这段代码中包含两种操作符’?.’和’??’，之前都没有看到过，突然想起node14版本已经出来很久了，立马去翻了一下新版本的文档，果然这两个操作符都是为了解决以前开发中很经常遇到的两种问题。
Nodejs14重点功能介绍Optional Chaining官方介绍节选The optional chaining operator (?.) enables you to read the value of a property located deep within a chain of connected objects without having to check ...</div></div></div><div class="recent-post-item"><div class="post_cover left_radius"><a href="/posts/10b18d71/" title="20210402-重庆游记"> <img class="post_bg" data-src="/upload/20210402%E9%87%8D%E5%BA%86%E6%B8%B8%E8%AE%B0/20210402_%E9%87%8D%E5%BA%86_12.jpg" onerror="this.onerror=null;this.src='/img/404.jpg'" alt="20210402-重庆游记"></a></div><div class="recent-post-info"><a class="article-title" href="/posts/10b18d71/" title="20210402-重庆游记">20210402-重庆游记</a><div class="article-meta-wrap"><time class="post-meta__date"><span class="post-meta__date-created" title="发表于 2021-04-26 14:06:44"><i class="far fa-calendar-alt"></i>2021-04-26</span><span class="article-meta__separator">|</span><span class="post-meta__date-updated" title="更新于 2021-04-26 14:38:42"><i class="fas fa-history"></i>2021-04-26</span></time><span class="article-meta"><span class="article-meta__separator">|</span><i class="fas fa-inbox article-meta__icon"></i><a class="article-meta__categories" href="/categories/%E6%97%85%E6%B8%B8%E6%97%A5%E8%AE%B0/">旅游日记</a></span><span class="article-meta tags"><span class="article-meta__separator">|</span><i class="fas fa-tag article-meta__icon"></i><a class="article-meta__tags" href="/tags/%E6%97%85%E6%B8%B8%E6%97%A5%E8%AE%B0/">旅游日记</a></span></div><div class="content">
待上传内容~（゜ー゜）
</div></div></div><div class="recent-post-item"><div class="post_cover right_radius"><a href="/posts/364d7e27/" title="字符串编码问题"> <img class="post_bg" data-src="/upload/homePage/20210426115900.jpg" onerror="this.onerror=null;this.src='/img/404.jpg'" alt="字符串编码问题"></a></div><div class="recent-post-info"><a class="article-title" href="/posts/364d7e27/" title="字符串编码问题">字符串编码问题</a><div class="article-meta-wrap"><time class="post-meta__date"><span class="post-meta__date-created" title="发表于 2021-04-26 13:51:30"><i class="far fa-calendar-alt"></i>2021-04-26</span><span class="article-meta__separator">|</span><span class="post-meta__date-updated" title="更新于 2021-04-26 14:27:15"><i class="fas fa-history"></i>2021-04-26</span></time><span class="article-meta"><span class="article-meta__separator">|</span><i class="fas fa-inbox article-meta__icon"></i><a class="article-meta__categories" href="/categories/uncategorized/">uncategorized</a></span><span class="article-meta tags"><span class="article-meta__separator">|</span><i class="fas fa-tag article-meta__icon"></i><a class="article-meta__tags" href="/tags/encode/">encode</a></span></div><div class="content">字符串编码问题我们已经讲过了，字符串也是一种数据类型，但是，字符串比较特殊的是还有一个编码问题。
因为计算机只能处理数字，如果要处理文本，就必须先把文本转换为数字才能处理。最早的计算机在设计时采用8个比特（bit）作为一个字节（byte），所以，一个字节能表示的最大的整数就是255（二进制11111111=十进制255），如果要表示更大的整数，就必须用更多的字节。比如两个字节可以表示的最大整数是65535，4个字节可以表示的最大整数是4294967295。
由于计算机是美国人发明的，因此，最早只有127个字符被编码到计算机里，也就是大小写英文字母、数字和一些符号，这个编码表被称为ASCII编码，比如大写字母A的编码是65，小写字母z的编码是122。
但是要处理中文显然一个字节是不够的，至少需要两个字节，而且还不能和ASCII编码冲突，所以，中国制定了GB2312编码，用来把中文编进去。
你可以想得到的是，全世界有上百种语言，日本把日文编到Shift_JIS里，韩国把韩文编到Euc-kr里，各国有各国的标准，就会不可避免地出现冲突，结果就是，在多语言混合的文本中，显示出来会有乱码。因此， ...</div></div></div><div class="recent-post-item"><div class="post_cover left_radius"><a href="/posts/a4fbff2c/" title="DBA题目索引设计问题调研"> <img class="post_bg" data-src="/upload/homePage/20210425115900.jpg" onerror="this.onerror=null;this.src='/img/404.jpg'" alt="DBA题目索引设计问题调研"></a></div><div class="recent-post-info"><a class="article-title" href="/posts/a4fbff2c/" title="DBA题目索引设计问题调研">DBA题目索引设计问题调研</a><div class="article-meta-wrap"><time class="post-meta__date"><span class="post-meta__date-created" title="发表于 2021-04-23 17:08:46"><i class="far fa-calendar-alt"></i>2021-04-23</span><span class="article-meta__separator">|</span><span class="post-meta__date-updated" title="更新于 2021-05-17 17:19:59"><i class="fas fa-history"></i>2021-05-17</span></time><span class="article-meta"><span class="article-meta__separator">|</span><i class="fas fa-inbox article-meta__icon"></i><a class="article-meta__categories" href="/categories/uncategorized/">uncategorized</a></span><span class="article-meta tags"><span class="article-meta__separator">|</span><i class="fas fa-tag article-meta__icon"></i><a class="article-meta__tags" href="/tags/Mysql/">Mysql</a></span></div><div class="content">题目本题目来源自网络，引用自cnblogs 05 | 深入浅出索引（下），最初出处因搜索结果过多目前无法确定。
DBA小吕在入职新公司的时候，就发现自己接手维护的库里面，有这么一个表，表结构定义类似这样的：
CREATE TABLE `geek` (`a` int(11) NOT NULL,`b` int(11) NOT NULL,`c` int(11) NOT NULL,`d` int(11) NOT NULL,PRIMARY KEY (`a`,`b`),KEY `c` (`c`),KEY `ca` (`c`,`a`),KEY `cb` (`c`,`b`)) ENGINE=InnoDB;
公司的同事告诉他说，由于历史原因，这个表需要a、b做联合主键，这个小吕理解了。
但是，学过本章内容的小吕又纳闷了，既然主键包含了a、b这两个字段，那意 ...</div></div></div><div class="recent-post-item"><div class="post_cover right_radius"><a href="/posts/4bdcd099/" title="Mysql优化减少回表操作"> <img class="post_bg" data-src="/upload/homePage/20210414152100.jpg" onerror="this.onerror=null;this.src='/img/404.jpg'" alt="Mysql优化减少回表操作"></a></div><div class="recent-post-info"><a class="article-title" href="/posts/4bdcd099/" title="Mysql优化减少回表操作">Mysql优化减少回表操作</a><div class="article-meta-wrap"><time class="post-meta__date"><span class="post-meta__date-created" title="发表于 2021-04-14 10:19:12"><i class="far fa-calendar-alt"></i>2021-04-14</span><span class="article-meta__separator">|</span><span class="post-meta__date-updated" title="更新于 2021-04-15 09:43:03"><i class="fas fa-history"></i>2021-04-15</span></time><span class="article-meta"><span class="article-meta__separator">|</span><i class="fas fa-inbox article-meta__icon"></i><a class="article-meta__categories" href="/categories/uncategorized/">uncategorized</a></span><span class="article-meta tags"><span class="article-meta__separator">|</span><i class="fas fa-tag article-meta__icon"></i><a class="article-meta__tags" href="/tags/Mysql/">Mysql</a></span></div><div class="content">情景有一张日增量的Mysql InnoDB数据表，未分库分表，ID为自增主键，DAY_TAG为非唯一索引，当前数据量为69660129，现需根据其数据做每日的统计报表，每日数据分段统计分析后写入另一张表，数据分段查询使用limit offset,rows。在此环境下，执行’select * from table where day_tag = ‘2021-04-14’ limit 20, 2’只需要几毫秒结果就返回了，但是若执行’select * from table where day_tag = ‘2021-04-14’ limit 300000, 2’，还是2条记录却会发现实际耗时很久。
问题分析虽然我们仅需2条记录，但实际Mysql对前300000条记录都进行了不必要的回表操作，导致耗时增加，我们只要减少回表操作就可以有效的优化查询的效率。
那么什么是回表操作呢？在这之前我们要先了解两个概念聚簇索引和非聚簇索引。
聚集索引（聚簇索引）：以 InnoDB 作为存储引擎的表，表中的数据都会有一个主键，即使你不创建主键，系统也会帮你创建一个隐式的主键。这是因为 InnoDB 是把数 ...</div></div></div><div class="recent-post-item"><div class="post_cover left_radius"><a href="/posts/98e85ae5/" title="解决爬取Https页面报unable to find valid certification path to requested target的问题"> <img class="post_bg" data-src="/upload/homePage/20200628154000.jpg" onerror="this.onerror=null;this.src='/img/404.jpg'" alt="解决爬取Https页面报unable to find valid certification path to requested target的问题"></a></div><div class="recent-post-info"><a class="article-title" href="/posts/98e85ae5/" title="解决爬取Https页面报unable to find valid certification path to requested target的问题">解决爬取Https页面报unable to find valid certification path to requested target的问题</a><div class="article-meta-wrap"><time class="post-meta__date"><span class="post-meta__date-created" title="发表于 2020-06-28 10:53:51"><i class="far fa-calendar-alt"></i>2020-06-28</span><span class="article-meta__separator">|</span><span class="post-meta__date-updated" title="更新于 2020-07-08 10:13:03"><i class="fas fa-history"></i>2020-07-08</span></time><span class="article-meta"><span class="article-meta__separator">|</span><i class="fas fa-inbox article-meta__icon"></i><a class="article-meta__categories" href="/categories/uncategorized/">uncategorized</a></span><span class="article-meta tags"><span class="article-meta__separator">|</span><i class="fas fa-tag article-meta__icon"></i><a class="article-meta__tags" href="/tags/https/">https</a><span class="article-meta__link">•</span><a class="article-meta__tags" href="/tags/%E8%AF%81%E4%B9%A6/">证书</a></span></div><div class="content">最近调试爬虫程序，对ershcimi进行爬取时报错，堆栈信息如下：</div></div></div><div class="recent-post-item"><div class="post_cover right_radius"><a href="/posts/c15a9847/" title="Mysql关于blob数据类型使用mysqldump导出乱码问题解决"> <img class="post_bg" data-src="/upload/homePage/20200611092200.jpg" onerror="this.onerror=null;this.src='/img/404.jpg'" alt="Mysql关于blob数据类型使用mysqldump导出乱码问题解决"></a></div><div class="recent-post-info"><a class="article-title" href="/posts/c15a9847/" title="Mysql关于blob数据类型使用mysqldump导出乱码问题解决">Mysql关于blob数据类型使用mysqldump导出乱码问题解决</a><div class="article-meta-wrap"><time class="post-meta__date"><span class="post-meta__date-created" title="发表于 2020-06-11 09:17:10"><i class="far fa-calendar-alt"></i>2020-06-11</span><span class="article-meta__separator">|</span><span class="post-meta__date-updated" title="更新于 2020-07-08 10:13:03"><i class="fas fa-history"></i>2020-07-08</span></time><span class="article-meta"><span class="article-meta__separator">|</span><i class="fas fa-inbox article-meta__icon"></i><a class="article-meta__categories" href="/categories/uncategorized/">uncategorized</a></span><span class="article-meta tags"><span class="article-meta__separator">|</span><i class="fas fa-tag article-meta__icon"></i><a class="article-meta__tags" href="/tags/Mysql/">Mysql</a></span></div><div class="content">情景最近查看服务器上的Mysql自动备份，发现关于blob数据类型使用mysqldump导出有乱码的情况，命令如下：
mysqldump -h$db_host -u$db_username -p$db_password --events --default-character-set=utf8 --all-databases | gzip > $backup_dir/mysql_dump_$today.sql.gz
原因分析看到有乱码，肯定第一时间怀疑是字符集的问题，但是又确认了一下utf8是没有问题的，而且发现乱码是因为包含blob类型字段，所以查了一下，原来少了个参数–hex-blob，看参数名应该是以二进制形式导出blob。
解决方案修改后的命令：
mysqldump -h$db_host -u$db_username -p$db_password --events --default-character-set=utf8 --hex-blob --all-databases | gzip > $backup_dir/mysq ...</div></div></div><nav id="pagination"><div class="pagination"><span class="page-number current">1</span><a class="page-number" href="/page/2/">2</a><span class="space">…</span><a class="page-number" href="/page/7/">7</a><a class="extend next" rel="next" href="/page/2/"><i class="fas fa-chevron-right fa-fw"></i></a></div></nav></div><div class="aside_content" id="aside_content"><div class="card-widget card-info"><div class="card-content"><div class="card-info-avatar is-center"><img class="avatar-img" src="/images/avatar.png" onerror="this.onerror=null;this.src='/img/friend_404.gif'" alt="avatar"/><div class="author-info__name">混饭</div><div class="author-info__description">重度拖延症患者(-__-)b</div></div><div class="card-info-data"><div class="card-info-data-item is-center"><a href="/archives"><div class="headline">文章</div><div 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