ab是apache自带的一个很好用的压力测试工具，当安装完apache的时候，就可以在bin下面找到ab
我们可以模拟100个并发用户，对一个页面发送1000个请求
./ab -n1000 -c100 http://www.cnblogs.com/pick/
其中-n代表请求数，-c代表并发数（ 详细参数可以用ab --help 查看）
返回结果:
##首先是apache的版本信息
This is ApacheBench, Version 2.3 <$Revision: 655654 $>
Copyright 1996 Adam Twiss, Zeus Technology Ltd, http://www.zeustech.net/
Licensed to The Apache Software Foundation, http://www.apache.org/
Benchmarking www.cnblogs.com (be patient)
Completed 100 requests
Completed 200 requests
Completed 300 requests
Completed 400 requests
Completed 500 requests
Completed 600 requests
Completed 700 requests
Completed 800 requests
Completed 900 requests
Completed 1000 requests
Finished 1000 requests
Server Software:
Server Hostname: www.cnblogs.com
Server Port: 80
Document Path: /pick/
Document Length: 40990 bytes
Concurrency Level: 100 ##并发数
Time taken for tests: 8.385 seconds ##共使用了多少时间
Complete requests: 1000 ##请求数
Failed requests: 616 ##失败请求
(Connect: 0, Receive: 0, Length: 616, Exceptions: 0)
Write errors: 0
Total transferred: 41420957 bytes ##总共传输字节数，包含http的头信息等
HTML transferred: 41111501 bytes ##html字节数，实际的页面传递字节数
Requests per second: 119.27 [#/sec] (mean) ##每秒多少请求，这个是非常重要的参数数值，服务器的吞吐量
Time per request: 838.456 [ms] (mean) ##用户平均请求等待时间
Time per request: 8.385 [ms] (mean, across all concurrent requests) ##服务器平均处理时间，也就是服务器吞吐量的倒数
Transfer rate: 4824.36 [Kbytes/sec] received ##每秒获取的数据长度
Connection Times (ms)
min mean[+/-sd] median max
Connect: 24 225 532.6 29 7028
Processing: 50 396 916.4 88 6164
Waiting: 25 133 473.9 31 3040
Total: 75 621 1095.1 129 7196
Percentage of the requests served within a certain time (ms)
50% 129 ## 50%的请求在129ms内返回
66% 164 ## 66%的请求在164ms内返回
75% 401
80% 1102
90% 1675
95% 3435
98% 4130
99% 4160
100% 7196 (longest request)
说明：考虑到带宽不在测试的范围，ab压力测试应该在内网测试。