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JavaScript 的性能优化：加载和执行

概览无论当前JavaScript代码是内嵌还是在外链文件中，页面的下载和渲染都必须停下来等待脚本执行完成。JavaScript执行过程耗时越久，浏览器等待响应用户输入的时间就越长。浏览器在下载和执行脚本时出现阻塞的原因在于，脚本可能会改变页面或JavaScript的命名空间，它们对后面页面内容造成影响。一个典型的例子就是在页面中使用document.write()。例如清单1清单1JavaScript代码内嵌示例Sou</span> <p class="auth-span"> <span class="muted"><i class="fa fa-user"></i><span class="zj-icon-text">系统</span></span> <span class="muted"><i class="fa fa-clock-o"></i><span class="zj-icon-text">2019-08-29 22:50:45</span></span> <span class="muted"><i class="fa fa-eye"></i><span class="zj-icon-text">3686</span></span>  </p> </article><article class="excerpt"> <header> <a title="DB2" class="label label-important zj-del-target" href="/category/48">DB2<i class="label-arrow"></i></a> <h2> <a class="zj-titles zj-del-target" href="/article/7375" title="db2 快照 SNAPSHOT" target="_blank" onclick="return recordId('',)">db2 快照 SNAPSHOT </a> </h2> </header> <div class="focus"> <a class="zj-del-target" href="/article/7375" target="_blank"><img style="width: 200px; height: 123px;" class="thumb" src="/Public/static/images/article/14.jpg" alt="" title=""></a> </div> <span class="note" onclick="if (jq.browser.versions.mobile) {window.location.href='/article/7375';}else{window.open('/article/7375');}" style="cursor: pointer;">打开和关闭快照缺省情况不打开DB2监控，必须在连接或实例级别上进行设置。有一系列监视器开关来决定是否监控某种数据元素。还预留了一个内存堆，用于包含为监控而存储的信息。1：在instance级别上设置监视器开关在实例级别上设置监视器开关会影响连接到该实例中任何数据库的所有用户。下面是监视器开关DFT_MON_STMT：语句监视器（用于动态SQL）DFT_MON_TABLE：表监视器DFT_MON_LOCK：锁监视器DFT_MON_BUFPOOL：缓冲池监视器</span> <p class="auth-span"> <span class="muted"><i class="fa fa-user"></i><span class="zj-icon-text">系统</span></span> <span class="muted"><i class="fa fa-clock-o"></i><span class="zj-icon-text">2019-08-12 01:54:05</span></span> <span class="muted"><i class="fa fa-eye"></i><span class="zj-icon-text">3685</span></span>  </p> </article><article class="excerpt"> <header> <a title="Python" class="label label-important zj-del-target" href="/category/44">Python<i class="label-arrow"></i></a> <h2> <a class="zj-titles zj-del-target" href="/article/30729" title="Python计算机视觉编程第六章——图像聚类(K-means聚类，DBSCAN" target="_blank" onclick="return recordId('',)">Python计算机视觉编程第六章——图像聚类(K-means聚类，DBSCAN </a> </h2> </header> <div class="focus"> <a class="zj-del-target" href="/article/30729" target="_blank"><img style="width: 200px; height: 123px;" class="thumb" src="/Public/static/images/article/8.jpg" alt="" title=""></a> </div> <span class="note" onclick="if (jq.browser.versions.mobile) {window.location.href='/article/30729';}else{window.open('/article/30729');}" style="cursor: pointer;">Python计算机视觉编程图像聚类（一）K-means聚类1.1SciPy聚类包1.2图像聚类1.1在主成分上可视化图像1.1像素聚类（二）层次聚类（三）谱聚类图像聚类聚类概念无监督学习：没有标签。（对于监督学习问题中，我们会被告知什么是正确答案，在无监督学习中，没有任何标签，或者都具有相同的标签，得到的数据如下图，图上有一系列点，但是它们没有标签，因此训练集可以写成{x(1),x(1),x(1),...,x(m)}\left\{x^{(1)},x^{(1</span> <p class="auth-span"> <span class="muted"><i class="fa fa-user"></i><span class="zj-icon-text">系统</span></span> <span class="muted"><i class="fa fa-clock-o"></i><span class="zj-icon-text">2019-09-27 17:56:55</span></span> <span class="muted"><i class="fa fa-eye"></i><span class="zj-icon-text">3684</span></span>  </p> </article><article class="excerpt"> <header> <a title="ASP.NET" class="label label-important zj-del-target" href="/category/56">ASP.NET<i class="label-arrow"></i></a> <h2> <a class="zj-titles zj-del-target" href="/article/21328" title="ASP.NET MVC模型绑定的6个建议" target="_blank" onclick="return recordId('',)">ASP.NET MVC模型绑定的6个建议 </a> </h2> </header> <div class="focus"> <a class="zj-del-target" href="/article/21328" target="_blank"><img style="width: 200px; height: 123px;" class="thumb" src="/Public/static/images/article/5.jpg" alt="" title=""></a> </div> <span class="note" onclick="if (jq.browser.versions.mobile) {window.location.href='/article/21328';}else{window.open('/article/21328');}" style="cursor: pointer;">ASP.NETMVC中的ModelBinding使用起来非常简单。你的Action方法需要数据，在传入的HTTP请求中携带着你需要的数据，数据可以在请求的表单数据中，还可能在你的URL地址本身中。通过DefaultModelBinder，可以神奇地将表单中的数据和路由中的数据转换到对象中。ModelBinder使得你的控制器代码可以干净地从请求以及关联的环境中分离出来。这里有一些关于在MVC项目中更好使用ModelBinding的建议。Tip#1:最好使用</span> <p class="auth-span"> <span class="muted"><i class="fa fa-user"></i><span class="zj-icon-text">系统</span></span> <span class="muted"><i class="fa fa-clock-o"></i><span class="zj-icon-text">2019-08-29 23:43:33</span></span> <span class="muted"><i class="fa fa-eye"></i><span class="zj-icon-text">3684</span></span>  </p> </article><article class="excerpt"> <header> <a title="Hadoop" class="label label-important zj-del-target" href="/category/60">Hadoop<i class="label-arrow"></i></a> <h2> <a class="zj-titles zj-del-target" href="/article/11775" title="Hadoop 的 TotalOrderPartitioner" target="_blank" onclick="return recordId('',)">Hadoop 的 TotalOrderPartitioner </a> </h2> </header> <div class="focus"> <a class="zj-del-target" href="/article/11775" target="_blank"><img style="width: 200px; height: 123px;" class="thumb" src="/Public/static/images/article/13.jpg" alt="" title=""></a> </div> <span class="note" onclick="if (jq.browser.versions.mobile) {window.location.href='/article/11775';}else{window.open('/article/11775');}" style="cursor: pointer;">http://blog.oddfoo.net/2011/04/17/mapreduce-partition%E5%88%86%E6%9E%90-2/Partition所处的位置Partition位置Partition主要作用就是将map的结果发送到相应的reduce。这就对partition有两个要求：1）均衡负载，尽量的将工作均匀的分配给不同的reduce。2）效率，分配速度一定要快。Mapreduce提供的PartitionerMapreduce默认的</span> <p class="auth-span"> <span class="muted"><i class="fa fa-user"></i><span class="zj-icon-text">系统</span></span> <span class="muted"><i class="fa fa-clock-o"></i><span class="zj-icon-text">2019-08-12 09:29:57</span></span> <span class="muted"><i class="fa fa-eye"></i><span class="zj-icon-text">3684</span></span>  </p> </article><article class="excerpt"> <header> <a title="编程技术" class="label label-important zj-del-target" href="/category/30">编程技术<i class="label-arrow"></i></a> <h2> <a class="zj-titles zj-del-target" href="/article/2013" title="CodeSmith学习笔记(二)：操作数据库" target="_blank" onclick="return recordId('',)">CodeSmith学习笔记(二)：操作数据库 </a> </h2> </header> <div class="focus"> <a class="zj-del-target" href="/article/2013" target="_blank"><img style="width: 200px; height: 123px;" class="thumb" src="/Public/static/images/article/5.jpg" alt="" title=""></a> </div> <span class="note" onclick="if (jq.browser.versions.mobile) {window.location.href='/article/2013';}else{window.open('/article/2013');}" style="cursor: pointer;">1.打开SchemaExploer配置数据库连接，定义表属性的Type为SchemaExplorer.TableSchema,数据库属性Type为SchemaExplorer.DatabaseSchema.2.定义内部的方法，下面调用用到的3.循环表的非主键4.定义输出到文件，枚举类型（头部定义属性时用到），常量。5.选择属性6.运行，结果如下CodeSmith学习笔记(二)：操作数据库</span> <p class="auth-span"> <span class="muted"><i class="fa fa-user"></i><span class="zj-icon-text">系统</span></span> <span class="muted"><i class="fa fa-clock-o"></i><span class="zj-icon-text">2019-08-12 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