Centos服务器测试压力我们可以使用Apache自带的压力测试的工具ab（ApacheBench），做一些简单的压力测试。
centos服务器安装ab工具。
yum install httpd-tools
执行压力测试命令：
ab -n 1000 -c 100 http://xx
-n 后面的1000代表总共发出1000个请求；-c后面的100表示采用100个并发（模拟100个人同时访问），后面的网址表示测试的目标URL。
[root@Tomcat ab]# ab -c 1000 -n 4000 http://192.168.0.222/docs/manager-howto.html
This is ApacheBench, Version 2.0.40-dev <$Revision: 1.146 $> apache-2.0
Copyright 1996 Adam Twiss, Zeus Technology Ltd, http://www.zeustech.net/
Copyright 2006 The Apache Software Foundation, http://www.apache.org/
Benchmarking 192.168.0.222 (be patient)
Completed 400 requests
Completed 800 requests
Completed 1200 requests
Completed 1600 requests
Completed 2000 requests
Completed 2400 requests
Completed 2800 requests
Completed 3200 requests
Completed 3600 requests
Finished 4000 requests
Server Software: nginx/1.4.3
Server Hostname: 192.168.0.222
Server Port: 80
Document Path: /docs/manager-howto.html
Document Length: 73924 bytes
Concurrency Level: 1000
Time taken for tests: 0.875928 seconds
Complete requests: 4000
Failed requests: 0
Write errors: 0
Total transferred: 296732000 bytes
HTML transferred: 295696000 bytes
Requests per second: 4566.59 [#/sec] (mean)
#最重要的指标之一，相当于LR中的每秒事务数，后面括号中的mean表示这是一个平均值，越大抗压越强
Time per request: 218.982 [ms] (mean)
#最重要的指标之二，相当于LR中的平均事务响应时间，后面括号中的mean表示这是一个平均值
Time per request: 0.219 [ms] (mean, across all concurrent requests)
Transfer rate: 330822.86 [Kbytes/sec] received
#平均每秒网络上的流量，吞吐量，越大抗压越强
Connection Times (ms)
min mean[+/-sd] median max
Connect: 0 0 4.5 0 29
Processing: 1 17 14.5 17 653
Waiting: 0 17 14.5 17 653
Total: 15 18 15.2 17 674
Percentage of the requests served within a certain time (ms)
50% 17
66% 18
75% 18
80% 18
90% 20
95% 22
98% 37
99% 40
100% 674 (longest request)
