# 首次分析

现在我们可以开始分析应用了。

Now we're ready to profile the application.

我们先分析 clone 下来的项目中的第一段服务器代码 1-server-with-slow-function.js。

Let's try with the first server in the repo, 1-server-with-slow-function.js.

该代码使用 express 启动了一个 HTTP 服务器，服务器具有一个根路由 /，在渲染页面前执行一定操作。

It contains an HTTP server, built using Express with a root route (/) that performs some work before rendering a landing page.

该服务器可以直接通过执行 node 1-server-with-slow-function.js 启动，然后用浏览器打开 http://localhost:3000/。如果你看到页面中显示 "Hello World" 说明没有问题。

The server can be started with node 1-server-with-slow-function.js and then accessed in the browser at http://localhost:3000/. If the landing page says "Hello World" then things are working!

我们试着用 Flame 分析这个服务器，看看我们是否能找到代码中的瓶颈。

Let's try and profile the server with Flame to see if we can find any bottlenecks.

在开始之前，我们还需要一个 http 压测工具。

To do that we need a tool that can simulate sufficiently intense HTTP load.

建议使用 autocannon，它支持 Windows、Mac 以及 Linux，并且开箱即用。

We suggest autocannon which is supported on Windows, Mac and Linux and is straightforward to use.

通过 npm 安装 autocannon：

Let's install it from npm:

npm install -g autocannon

为了运行分析，我们使用 Flame 运行服务器，当服务器准备就绪时，即开始侦听端口时，再用 autocannon 向它发送大量请求。

To run the analysis we want to run the server with Flame and when the server is ready - i.e. starts listening on a port - we want to send a ton of requests to it using autocannon.

这些操作都可以使用单个命令执行，可以按原样复制和粘贴：

All that can be performed with a single command, which can be copied and pasted as-is:

clinic flame --on-port 'autocannon localhost:$PORT' -- node 1-server-with-slow-function.js

我们拆分一下这个命令：

Let's break this command down:

• clinic flame 调用 flame 命令行工具。

The clinic flame portion invokes the flame command tool.

• --on-port 参数指定在服务开始监听端口后马上执行的脚本，即 autocannon localhost:$PORT。

The --on-port flag will execute the supplied script as soon as the server starts listening on a port.

• 脚本中的 $PORT 变量是服务器开始侦听的第一个端口。

The $PORT variable in that script is set to the first port that the server began listening on.

• -- 后面的命令用于启动我们要分析的服务，比如这里的 node 1-server-with-slow-function.js。

Everything after the double-dash (--) is the command which starts the server that we want to profile, in this case node 1-server-with-slow-function.js.

这行命令会运行三个可执行文件：父可执行文件 clinic flame, --on-port 中的可执行文件 autocannon，以及可执行文件 Node。

This one command runs three executables: the clinic flame parent executable, the autocannon executable in --on-port and the node executable.

运行该命令后，将对该进程进行 10 秒的负载测试（10 秒是 autocannon 的默认测试持续时间），然后将结果输出为 HTML 文件，并在浏览器中自动打开的。

Upon running the command, the process will be load tested for 10 seconds (as per the autocannon default duration), then the results be compiled into a single HTML file that should automatically open in the browser.

生成的 HTML 会被渲染为下面的这样：

The resulting HTML should look similar to the following:

这就是所谓的火焰图。

This is known as a Flamegraph.