评估网页性能工具--Page Speed

什么是 Page Speed？
Page Speed 是开源 Firefox/Firebug 插件。网站管理员和网络开发人员可以使用 Page Speed 来评估他们网页的性能，并获得有关如何改进性能的建议。
   
Page Speed 是如何工作的？
Page Speed 对网站的网络服务器配置和前端代码执行若干测试。这些测试基于一组已知可增强网页性能的最佳实践。在网页上运行 Page Speed 的网站管理员会获得一组针对各网页的分数，以及有关如何改善网页性能的有用建议。
   
为什么要使用 Page Speed？
利用 Page Speed，您可以：
    * 使您的网站更快速。
    * 使互联网用户始终关注您的网站。
    * 减少您的带宽成本和托管成本。
    * 改善网络！

运行Page Speed
为了生成最精确的结果，你应该等待完全加载页面后再使用Page Speed。也可以激活“Automatically run at onload option”选项。
1. 打开Firefox浏览器
2. 选择工具-Tools > Firebug > Open Firebug
3. 在Firebug窗口中，选择Page Speed 标签页
4. 打开你需要的网站地址，等待完全加载完出现“Done”
5. 点击”Analyze Performance“

Here's how to interpret the color-code scores:

• High priority. These suggestions represent the largest potential performance wins for relatively little development effort. You should address these items first.
  
• Medium priority. These suggestions may represent smaller wins or much more work to implement. You should address these items next.
  
• Working fine or low priority. If suggestions are displayed, as indicated with a + sign, they probably represent minor wins. You should only be concerned with these items after you've handled the higher-priority ones.
• Informational messages only. Either these items don't apply to this page or there was a problem in running the test.

  Tip:If your results show a large number of informational messages, this is likely because you tried to analyze the page before it was fully loaded. ClickRefresh Analysisto rerun the analysis.

Recording activity
在使用此功能前，先禁用HTTPWATCH。
1. 重新启动Firefox并关闭页面。
2. 清除浏览缓存。
3. 清除之前所有录制的Browser activity，在地址栏上进入一个空白页。
4. 选择Tools > Firebug > Open Firebug
5. 在Firebug窗口中，选择Page Speed Activity标签页
6. 点击“Record Activity”

7. 打开你需要的网站地址，此页面会加载一段时间。
8. 关闭停止录制。

Network events		Description
	DNS	The browser is performing a DNS lookup for this resource
	Wait	The browser is waiting to establish a network (TCP) connection with the web server. Because the browser limits the number of connections it can keep open, if it has reached its maximum, it must wait until one is closed to begin a new one. (For information on browser connections, seeParallel downloads across hostnames.) This event shows the time the browser waits until another completes.
	Connect	The browser is establishing a network (TCP) connection with the web server. This event only appears for new connections; not for connections that are reused.
	Send	The browser has sent the HTTP request. Only GET requests are shown.
	Connected	The browser is waiting for data over the network. The event ends when the browser ends the TCP connection. Resources that show lengthy Connected events may benefit from optimization to reduce payload size, such as compression
Local events		Description
	Cache Hit	The browser has successfully located the resource in its cache.
	Data Available	Data has been made available to the browser for parsing. As web servers send out data in chunks, many of these events may appear for a single resource, if it is a large file.
	Paint	The browser is rendering elements on the page.
	JS Parse	The browser is parsing JavaScript. This event can overlap with other events; where it does, it is shown in a sub-row for that resource.
	JS Execute	The browser is executing JavaScript. This event can overlap with other events; where it does, it is shown in a sub-row for that resource. If you see a substantial delay between the JS Parse and JS Execute events, this indicates that the resource contains functions that may be deferrable.