目标
估算网站系统，峰值 RPS。
概念
PV: page view，即页面被浏览的次数。
RPS: Requests per second，即每秒请求次数。
关于 QPS/RPS 概念，详见 如何使用 sysbench 对 RDS进行压力测试？
峰值 RPS
原理：按照二八原则，网站每天 80%的访问量集中在 20% 的时间里，这20%时间叫做峰值时间。
公式：( 总PV数 * 80% ) / ( 每天秒数 * 20% ) = 峰值时间每秒请求数(RPS)。
机器：峰值时间每秒 RPS / 单台机器的RPS = 需要的机器。
举个栗子
假设，某 Web系统每天有 1000万 PV访问量，这个网站需要准备多少 RPS？
RPS: ( 10000000 * 0.8 ) / (86400 * 0.2 ) = 463
再假设，经过测试单台服务器有效处理能力为 100 RPS，需要多少服务器？
服务器: 463 / 100 = 5台
使用 ab 压力测试
使用 apche ab 工具，对某项目网站Web系统进行压测，共4次每次间隔 5分钟。
1. 测试过程
第1次测试，请求:1000 并发:100 RPS: 1048/s 平均等待时间: 95.463 /ms
ab -n 1000 -c 100
...省略
Benchmarking (be patient)
Completed 100 requests
...省略
Completed 1000 requests
Finished 1000 requests
Server Software:
Server Hostname:
Server Port: 443
SSL/TLS Protocol: TLSv1.2,ECDHE-RSA-AES128-GCM-SHA256,2048,128
Document Path: /passport/login
Document Length: 10668 bytes
Concurrency Level: 100
Time taken for tests: 0.955 seconds
Complete requests: 1000
Failed requests: 0
Write errors: 0
Total transferred: 11242000 bytes
HTML transferred: 10668000 bytes
Requests per second: 1047.53 [#/sec] (mean)
Time per request: 95.463 [ms] (mean)
Time per request: 0.955 [ms] (mean, across all concurrent requests)
Transfer rate: 11500.28 [Kbytes/sec] received
Connection Times (ms)
min mean[+/-sd] median max
Connect: 8 48 45.2 36 320
Processing: 9 43 11.7 45 94
Waiting: 9 38 11.1 40 90
Total: 19 91 45.9 83 361
Percentage of the requests served within a certain time (ms)
50% 83
...省略
99% 319
100% 361 (longest request)
第2次测试，请求:1000 并发:200 RPS: 951.34/s 平均等待时间: 210.231/ms
ab -n 1000 -c 200
...省略
Benchmarking
Completed 100 requests
...省略
Completed 1000 requests
Finished 1000 requests
Server Software:
Server Hostname:
Server Port: 443
SSL/TLS Protocol: TLSv1.2,ECDHE-RSA-AES128-GCM-SHA256,2048,128
Document Path: /passport/login
Document Length: 10668 bytes
Concurrency Level: 200
Time taken for tests: 1.051 seconds
Complete requests: 1000
Failed requests: 0
Write errors: 0
Total transferred: 11242000 bytes
HTML transferred: 10668000 bytes
Requests per second: 951.34 [#/sec] (mean)
Time per request: 210.231 [ms] (mean)
Time per request: 1.051 [ms] (mean, across all concurrent requests)
Transfer rate: 10444.26 [Kbytes/sec] received
Connection Times (ms)
min mean[+/-sd] median max
Connect: 7 88 80.8 61 519
Processing: 9 76 36.8 84 299
Waiting: 8 54 30.5 49 247
Total: 16 164 90.7 162 567
Percentage of the requests served within a certain time (ms)
50% 162
...省略
99% 399
100% 567 (longest request)
第3次测试，请求:1000 并发:300 RPS: 806.40/s 平均等待时间: 372.023/ms
ab -n 1000 -c 300 https://www.demo.com/passport/login
...省略
Benchmarking www.demo.com (be patient)
Completed 100 requests
...省略
Finished 1000 requests
Server Software:
Server Hostname:
Server Port: 443
SSL/TLS Protocol: TLSv1.2,ECDHE-RSA-AES128-GCM-SHA256,2048,128
Document Path: /passport/login
Document Length: 10668 bytes
Concurrency Level: 300
Time taken for tests: 1.240 seconds
Complete requests: 1000
Failed requests: 0
Write errors: 0
Total transferred: 11242000 bytes
HTML transferred: 10668000 bytes
Requests per second: 806.40 [#/sec] (mean)
Time per request: 372.023 [ms] (mean)
Time per request: 1.240 [ms] (mean, across all concurrent requests)
Transfer rate: 8853.09 [Kbytes/sec] received
Connection Times (ms)
min mean[+/-sd] median max
Connect: 8 131 124.2 94 1009
Processing: 9 117 52.1 116 433
Waiting: 9 64 43.2 51 263
Total: 18 249 140.9 201 1041
Percentage of the requests served within a certain time (ms)
50% 201
...省略
99% 757
100% 1041 (longest request)
第4次测试，请求:5000 并发:100 RPS: 589.81/s 平均等待时间: 169.546/ms 其它: 出现 SSL握手失败。
ab -n 5000 -c 100 https://www.demo.com/passport/login
...省略
Benchmarking www.demo.com (be patient)
Completed 500 requests
...省略
Completed 3000 requests
SSL handshake failed (5).
...省略
Finished 5000 requests
Server Software:
Server Hostname:
Server Port: 443
SSL/TLS Protocol: TLSv1.2,ECDHE-RSA-AES128-GCM-SHA256,2048,128
Document Path: /passport/login
Document Length: 10668 bytes
Concurrency Level: 100
Time taken for tests: 8.477 seconds
Complete requests: 5000
Failed requests: 1
(Connect: 0, Receive: 0, Length: 1, Exceptions: 0)
Write errors: 0
Total transferred: 56198758 bytes
HTML transferred: 53329332 bytes
Requests per second: 589.81 [#/sec] (mean)
Time per request: 169.546 [ms] (mean)
Time per request: 1.695 [ms] (mean, across all concurrent requests)
Transfer rate: 6473.94 [Kbytes/sec] received
Connection Times (ms)
min mean[+/-sd] median max
Connect: 0 130 305.0 13 3019
Processing: 5 29 47.7 17 823
Waiting: 8 27 41.7 16 622
Total: 5 160 310.5 34 3035
Percentage of the requests served within a certain time (ms)
50% 34
...省略
99% 1246
100% 3035 (longest request)
2. 测试小结
a. 压测端与服务器端，在相同的网络，所以网络带宽不是瓶颈。
b. RPS 随着并发数的增加而减少，系统负载升高，CPU 成为瓶颈。
c. 平均等待时间，并发数成正比，即并发数量越大，用户等待时间越长，直到Web系统拒绝响应(见 SSL握手失败)
扩展: 测试原则&关键点
不同系统对最大负载的要求不一样。就通常的 web网站来说基本指标是：在合理的响应时间内，系统能提供最大的每秒请求数（QPS/RPS/TPS）。
1. 合理响应时间，3-5s是一个合格的网站渲染首屏最多花费的时间，如果单纯看最大qps而不管响应时间的话，这个测试是无意义的；
2. 每个页面包含的功能不一样多，所以指标也定不相同，那么访问最频繁的页面的性能指标应该是我们最关注的；
3. web网站大多读写急不平衡，但在有持续写入的情况下测试出来的指标与单纯读指标的对比，对判断锁的性能很有帮助；
4. 最重要的一点是，刚创业的站点应多注意快速开发业务，心里有性能这根弦，不犯愚蠢错误就足够了。等站点真正做出来再回头调优，应该是个甜蜜的过程。