ab是apache自带的一款功能强大的测试工具
安装了apache一般就自带了，
用法可以查看它的说明
$ ./ab
./ab: wrong number of arguments
Usage: ./ab [options] [http://]hostname[:port]/path
Options are:
-n requests Number of requests to perform
-c concurrency Number of multiple requests to make
-t timelimit Seconds to max. wait for responses
-p postfile File containing data to POST
-T content-type Content-type header for POSTing
-v verbosity How much troubleshooting info to print
-w Print out results in HTML tables
-i Use HEAD instead of GET
-x attributes String to insert as table attributes
-y attributes String to insert as tr attributes
-z attributes String to insert as td or th attributes
-C attribute Add cookie, eg. ‘Apache=1234. (repeatable)
-H attribute Add Arbitrary header line, eg. ‘Accept-Encoding: gzip’
Inserted after all normal header lines. (repeatable)
-A attribute Add Basic WWW Authentication, the attributes
are a colon separated username and password.
-P attribute Add Basic Proxy Authentication, the attributes
are a colon separated username and password.
-X proxy:port Proxyserver and port number to use
-V Print version number and exit
-k Use HTTP KeepAlive feature
-d Do not show percentiles served table.
-S Do not show confidence estimators and warnings.
-g filename Output collected data to gnuplot format file.
-e filename Output CSV file with percentages served
-h Display usage information (this message)
参数众多，一般我们用到的是-n 和-c
例如：
./ab -c 1000 -n 100
http://www.vpser.net/index.php
这个表示同时处理1000个请求并运行100次index.php文件.
