【IT168 技术文章】
引子
按照原定计划，今天开始研究 JMeter，一天的时间看完了大半的 User Manual，发现原来只要沉住气，学习效率还是蛮高的，而且大堆的英文文档也没有那么可怕。
本来想顺便把文档翻译一下，不过后来想了想，看懂是一回事，全部翻译出来又是另外一回事了，工作量太大，而且这也不是我一开始要研究 JMeter 的本意。不如大家有兴趣一起研究的遇到问题再一起讨论吧。
开源工具通常都是为了某个特定的目的而开发出来的，所以如果想找到一个开源的性能测试工具去与LoadRunner 或者 QALoad 之类去比较，实在有些勉强。但是开源工具也有它自己的优势：小巧、轻便，在自己擅长的领域可以提供优秀的解决方案。所以，我们可以考虑准备一个自己的“开源测试工具箱”，平时利用空闲时间了解各种工具所适用的环境和目的，知识慢慢积累下来以后，就可以在遇到问题时顺手拈来，轻松化解。
另外，如果8月份和9月份的空闲时间足够多，我想我会写一个系列文章来讲述在实际的开发和测试过程中引入开源性能测试工具的情况。如果有朋友感兴趣，希望大家可以一起研究和讨论。
简介
ab的全称是ApacheBench，是 Apache 附带的一个小工具，专门用于 HTTP Server 的benchmark testing，可以同时模拟多个并发请求。前段时间看到公司的开发人员也在用它作一些测试，看起来也不错，很简单，也很容易使用。
通过下面的一个简单的例子和注释，相信大家可以更容易理解这个工具的使用。
一个简单的例子
在这个例子的一开始，我执行了这样一个命令 ab -n 10 -c 10 http://www.google.com/
这个命令的意思是启动 ab ，模拟10个用户(-n 10)同时访问 www.google.com ，并迭代10次(-c 10)。跟着下面的是 ab 输出的测试报告，红色部分是我添加的注释。
更多信息
ab 不像 LR 那么强大，但是它足够轻便，如果只是在开发过程中想检查一下某个模块的响应情况，或者做一些场景比较简单的测试，ab 还是一个不错的选择——至少不用花费很多时间去学习 LR 那些复杂的功能，就更别说那 License 的价格了。
下面是 ab 的详细参数解释。
ab [ -A auth-username:password ] [ -c concurrency ] [ -C cookie-name=value ] [ -d ] [ -e csv-file ] [ -g gnuplot-file ] [ -h ] [ -H custom-header ] [ -i ] [ -k ] [ -n requests ] [ -p POST-file ] [ -P proxy-auth-username:password ] [ -q ] [ -s ] [ -S ] [ -t timelimit ] [ -T content-type ] [ -v verbosity] [ -V ] [ -w ] [ -x <table>-attributes ] [ -X proxy[:port] ] [ -y <tr>-attributes ] [ -z <td>-attributes ] [http://]hostname[:port]/path
-A auth-username:password
Supply BASIC Authentication credentials to the server. The username and password are separated by a single : and sent on the wire base64 encoded. The string is sent regardless of whether the server needs it (i.e., has sent an 401 authentication needed).
-c concurrency
Number of multiple requests to perform at a time. Default is one request at a time.
-C cookie-name=value
Add a Cookie: line to the request. The argument is typically in the form of a name=value pair. This field is repeatable.
-d
Do not display the "percentage served within XX [ms] table". (legacy support).
-e csv-file
Write a Comma separated value (CSV) file which contains for each percentage (from 1% to 100%) the time (in milliseconds) it took to serve that percentage of the requests. This is usually more useful than the 'gnuplot' file; as the results are already 'binned'.
-g gnuplot-file
Write all measured values out as a 'gnuplot' or TSV (Tab separate values) file. This file can easily be imported into packages like Gnuplot, IDL, Mathematica, Igor or even Excel. The labels are on the first line of the file.
-h
Display usage information.
-H custom-header
Append extra headers to the request. The argument is typically in the form of a valid header line, containing a colon-separated field-value pair (i.e., "Accept-Encoding: zip/zop;8bit").
-i
Do HEAD requests instead of GET.
-k
Enable the HTTP KeepAlive feature, i.e., perform multiple requests within one HTTP session. Default is no KeepAlive.
-n requests
Number of requests to perform for the benchmarking session. The default is to just perform a single request which usually leads to non-representative benchmarking results.
-p POST-file
File containing data to POST.
-P proxy-auth-username:password
Supply BASIC Authentication credentials to a proxy en-route. The username and password are separated by a single : and sent on the wire base64 encoded. The string is sent regardless of whether the proxy needs it (i.e., has sent an 407 proxy authentication needed).
-q
When processing more than 150 requests, ab outputs a progress count on stderr every 10% or 100 requests or so. The -q flag will suppress these messages.
-s
When compiled in
