徹底瞭解 ab 測試的計算公式

lyxxxh發表於2020-06-08

測試公式

[xxh@xxh-vmwarevirtualplatform code]$ ab -n 10 -c 3 http://lum2.test/ 
This is ApacheBench, Version 2.3 <$Revision: 1874286 $>
Copyright 1996 Adam Twiss, Zeus Technology Ltd, http://www.zeustech.net/
Licensed to The Apache Software Foundation, http://www.apache.org/

Benchmarking lum2.test (be patient).....done


Server Software:        nginx/1.18.0
Server Hostname:        lum2.test
Server Port:            80

Document Path:          /
Document Length:        39 bytes

Concurrency Level:      3
Time taken for tests:   0.009 seconds
Complete requests:      10
Failed requests:        0
Total transferred:      2730 bytes
HTML transferred:       390 bytes
Requests per second:    1175.78 [#/sec] (mean)
Time per request:       2.552 [ms] (mean)
Time per request:       0.851 [ms] (mean, across all concurrent requests)
Transfer rate:          313.46 [Kbytes/sec] received

Connection Times (ms)
              min  mean[+/-sd] median   max
Connect:        0    0   0.1      0       0
Processing:     2    2   0.3      2       3
Waiting:        2    2   0.3      2       3
Total:          2    2   0.3      2       3

Percentage of the requests served within a certain time (ms)
  50%      2
  66%      2
  75%      2
  80%      2
  90%      3
  95%      3
  98%      3
  99%      3
 100%      3 (longest request)

ab -n 10 -c 3 http://lum2.test

公式需要的關鍵變數

[Complete requests] 請求數（成功的）       10
[Time taken for tests] 花費時間    0.009
[Concurrency Level] 併發數         3
......

qps計算

公式: qps = 請求數 / 花費時間 

公式: [Requests per second] = [Complete requests] / [Time taken for tests]

結果: 10 / 0.009 = 1111.11111....

為什麼qps不是1175.78? 而是 1111.11….

因為[Time taken for tests] 被四捨五入了。

Time per request (第一個)

公式: tpr(1) = 併發數 * 花費時間 * 1000 / 請求數`
公式: tpr(1) = [Concurrency Level] * [Time taken for tests] * 1000 / [Complete requests] `
結果: 3 * 0.009 * 1000 / 10 = 2.7

(為什麼不是2.5? 因為誤差 上面已介紹)

Time per request (第二個)

公式: tpr(2) =  花費時間 * 1000 / 請求數`
公式: tpr(2) =  [Time taken for tests] * 1000 / [Complete requests]
結果: 0.009 * 1000 / 10 = 0.009

ab原始碼

   變數解釋:
    done 請求數
    timetaken  花費時間
    concurrency 併發數

   //qps
   printf("Requests per second:    %.2f [#/sec] (mean)\n",
               (double) done / timetaken);

    //tpr(1)
    printf("Time per request:       %.3f [ms] (mean)\n",
               (double) concurrency * timetaken * 1000 / done);
   //tpr(2) 
   printf("Time per request:       %.3f [ms] (mean, across all concurrent      requests)\n",(double) timetaken * 1000 / done);