例： ./ab -c 100 -n 10000 http://127.0.0.1/index.php

-c 100 即：每次并发100个
-n 10000 即： 共发送10000个请求

2. 测试结果分析

[junjie2@login htdocs]$ /data1/apache/bin/ab -c 1000 -n 50000 "http://10.10.10.10/a.php "
This is ApacheBench, Version 1.3d <$Revision: 1.73 $> apache-1.3
Copyright (c) 1996 Adam Twiss, Zeus Technology Ltd, http://www.zeustech.net/ 
Copyright (c) 1998-2002 The Apache Software Foundation, http://www.apache.org/

Benchmarking 10.65.129.21 (be patient)
Completed 5000 requests
Completed 10000 requests
Completed 15000 requests
Completed 20000 requests
Completed 25000 requests
Completed 30000 requests
Completed 35000 requests
Completed 40000 requests
Completed 45000 requests
Finished 50000 requests
Server Software: Apache/1.3.33 
Server Hostname: 10.65.129.21
Server Port: 80

Document Path: /a.php //请求的资源
Document Length: 0 bytes // 文档返回的长度，不包括相应头

Concurrency Level: 1000 // 并发个数
Time taken for tests: 48.650 seconds //总请求时间 
Complete requests: 50000 // 总请求数
Failed requests: 0 //失败的请求数
Broken pipe errors: 0
Total transferred: 9750000 bytes
HTML transferred: 0 bytes
Requests per second: 1027.75 [#/sec] (mean) // 平均每秒的请求数
Time per request: 973.00 [ms] (mean) // 平均每个请求消耗的时间
Time per request: 0.97 [ms] (mean, across all concurrent requests) // 就是上面的时间 除以并发数
Transfer rate: 200.41 [Kbytes/sec] received // 时间传输速率

Connnection Times (ms)
min mean[+/-sd] median max
Connect: 0 183 2063.3 0 45003
Processing: 28 167 770.6 85 25579
Waiting: 21 167 770.6 85 25578
Total: 28 350 2488.8 85 48639

Percentage of the requests served within a certain time (ms)
50% 85 // 就是有50%的请求都是在85ms内完成的
66% 89
75% 92
80% 96
90% 168
95% 640
98% 984
99% 3203
100% 48639 (last request)

3. 用127.0.0.1来访问可以排除网络的因素，不过在Linux上用本机的对外ip访问也是不走网卡，没有网络消耗的

ab 帮助：

1.  我们知道用ab测试时，最大并发不能超过1024，其实ab本身没有做这个限制，而是系统限制每个进程打开的最大的文件数为1024，ulimit查看如下：

[root@localhost ~]# ulimit -a
core file size          (blocks, -c) 0
data seg size           (kbytes, -d) unlimited
file size               (blocks, -f) unlimited
pending signals                 (-i) 1024
max locked memory       (kbytes, -l) 32
max memory size         (kbytes, -m) unlimited
open files                      (-n) 1024 
pipe size            (512 bytes, -p) 8
POSIX message queues     (bytes, -q) 819200
stack size              (kbytes, -s) 10240
cpu time               (seconds, -t) unlimited
max user processes              (-u) 32765
virtual memory          (kbytes, -v) unlimited
file locks                      (-x) unlimited

而且open files这个选项在一般的系统里是不允许修改成无限制的，如下：
[root@localhost ~]# ulimit -n unlimited
bash: ulimit: open files: cannot modify limit: Operation not permitted

但是稍微修改大一些或者是小一些，还是允许的，我们修改的小一些试试：
[root@localhost ~]# ulimit -n 1020
[root@localhost ~]# ulimit -n
1020
[root@localhost ~]#

在用ab测试，错误如下：

socket(PF_INET, SOCK_STREAM, IPPROTO_IP) = 1019 
ioctl(1019, FIONBIO, [1])               = 0
gettimeofday({1243919682, 867688}, NULL) = 0
connect(1019, {sa_family=AF_INET, sin_port=htons(80), sin_addr=inet_addr("10.55.38.18")}, 16) = -1 EINPROGRESS (Operation now in progress)
socket(PF_INET, SOCK_STREAM, IPPROTO_IP) = -1 EMFILE (Too many open files )
close(-1)                               = -1 EBADF (Bad file descriptor)
第1019个还能正常打开，下一个就报Too many open files的 错误了

确实有效，那么我们修改大一些吧：

[root@localhost ~]# ulimit -n 10240
[root@localhost ~]# ulimit -n
10240
[root@localhost ~]#

但是我们发现改大却不行，这里却冒出了一个AF_AX25 的名词：
socket(PF_INET, SOCK_STREAM, IPPROTO_IP) = 1024
ioctl(1024, FIONBIO, [1])               = 0
gettimeofday({1243919592, 254950}, NULL) = 0
connect(1024, {sa_family=AF_INET , sin_port=htons(80), sin_addr=inet_addr("10.55.38.18")}, 16) = -1 EINPROGRESS (Operation now in progress)
socket(PF_INET, SOCK_STREAM, IPPROTO_IP) = 1025
ioctl(1025, FIONBIO, [1])               = 0
gettimeofday({1243919592, 255242}, NULL) = 0
connect(1025, {sa_family=AF_AX25 , sa_data="http://www.mamicode.com/0P/n7&/22/0/0/0/0/0/0/0/0"}, 16) = -1 EAFNOSUPPORT (Address family not supported by protocol)

这个AF_AX25可能是buffer溢出造成的，但不确定哦：）。

另： 
-n 可以指定最大请求数，但是也不能超过50000哦：）
-v n   当n>=2 时，可以显示发送的http请求头，和响应的http头及内容； 压力测试时不要这么做哦：）

apache的ab命令做压力测试