参数说明：
-n 10 表示总请求数为10，共发出了10次请求
-c 10 表示并发用户数为10,同时有10个用户访问
http://www.xxx.com/ 表示这些请求的目标URL (注意，目标地址后面一定要加结束的反斜杠/)
关注的参数：
Requests per second：每秒的请求量，所谓的吞吐率。【这个值越小越好】
Time per request: 3466.517 [ms] (mean) 平均请求等待时间，也是吞吐率（用户等待的时间） mean表示平均值
Time per request: 346.652 [ms] (mean, across all concurrent requests) 服务器平均请求响应时间 在并发量为1时 用户等待时间相同 【这个值越大越好】
简单总结下：
Requests per second 的值越小越好，Time per request 的值越大越好
wangkongming@Vostro /etc/apache2 $ ab -n 10 -c 10 http://www.xxx.com/
This is ApacheBench, Version 2.3 <$Revision: 1528965 $>
Copyright 1996 Adam Twiss, Zeus Technology Ltd, http://www.zeustech.net/
Licensed to The Apache Software Foundation, http://www.apache.org/
Benchmarking www.xxx.com (be patient).....done
Server Software: Apache-Coyote/1.1
Server Hostname: www.xxx.com
Server Port: 80
Document Path: /
Document Length: 521 bytes // 请求的页面大小
Concurrency Level: 10 //并发量
Time taken for tests: 3.467 seconds //测试总共耗时
Complete requests: 10 //完成的请求
Failed requests: 9 //失败的请求
(Connect: 0, Receive: 0, Length: 9, Exceptions: 0)
Total transferred: 880759 bytes //总共传输数据量
HTML transferred: 871360 bytes
Requests per second: 2.88 [#/sec] (mean) //每秒钟的请求量。（仅仅是测试页面的响应速度）
Time per request: 3466.517 [ms] (mean) //等于 Time taken for tests/(complete requests/concurrency level) 即平均请求等待时间（用户等待的时间）
Time per request: 346.652 [ms] (mean, across all concurrent requests) //等于 Time taken for tests/Complete requests 即服务器平均请求响应时间 在并发量为1时 用户等待时间相同
Transfer rate: 248.12 [Kbytes/sec] received //平均每秒多少K，即带宽速率
Connection Times (ms)
min mean[+/-sd] median max
Connect: 31 34 2.6 35 39
Processing: 2 1962 909.4 2298 3432
Waiting: 2 336 528.4 67 1528
Total: 33 1996 910.9 2337 3466
Percentage of the requests served within a certain time (ms)
50% 2337
66% 2467
75% 2497
80% 2588
90% 3466
95% 3466
98% 3466
99% 3466
100% 3466 (longest request)
