gistfile1.txt

I wrote a simple PHP script to simulate activity (sleep for 500ms).  I set up a vhost to handle PHP requests via mod_fcgid. I 
- used PHP5.2, PHP5.3, PHP5.4 -- doesn't seem to matter. 
- used the latest trunk snapshot of mod_fcgid (2.3.8), and that didn't change behavior 
- used Apache 2.2.22 (and 2.2.17) with both worker and prefork mpms

Trying to figure out how to prevent serialized blocking of requests  in mod_fcgid.


test.php script:

usleep(500000);
echo $_SERVER['SCRIPT_FILENAME']." :: ".$_SERVER['SERVER_NAME'];


o Loaded Apache with the worker MPM.. Used a concurrency level of 2, feeding 10 requests, we see a bottleneck due to serialization:

Concurrency Level:      2
Time taken for tests:   3.116 seconds
Complete requests:      10
Failed requests:        0
Write errors:           0
Total transferred:      1560 bytes
HTML transferred:       0 bytes
Requests per second:    3.21 [#/sec] (mean)
Time per request:       623.257 [ms] (mean)
Time per request:       311.628 [ms] (mean, across all concurrent requests)
Transfer rate:          0.49 [Kbytes/sec] received

Connection Times (ms)
              min  mean[+/-sd] median   max
Connect:        3    3   0.2      3       3
Processing:   504  619 336.6    505    1574
Waiting:      504  619 336.6    505    1574
Total:        507  622 336.6    508    1577

Percentage of the requests served within a certain time (ms)
  50%    508
  66%    508
  75%    508
  80%    577
  90%   1577
  95%   1577
  98%   1577
  99%   1577
 100%   1577 (longest request)

o Once the processes are spun up however, we see 500ms (+~10ms overhead) for all requests as long as our concurrency does not exceed the number of child processes available

USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
apache   30209  0.0  0.4  57132  8488 ?        S    15:30   0:00 /usr/bin/php-cgi
apache   30214  0.0  0.4  57132  8480 ?        S    15:30   0:00 /usr/bin/php-cgi


Concurrency Level:      2
Time taken for tests:   2.546 seconds
Complete requests:      10
Failed requests:        0
Write errors:           0
Total transferred:      1560 bytes
HTML transferred:       0 bytes
Requests per second:    3.93 [#/sec] (mean)
Time per request:       509.200 [ms] (mean)
Time per request:       254.600 [ms] (mean, across all concurrent requests)
Transfer rate:          0.60 [Kbytes/sec] received

Connection Times (ms)
              min  mean[+/-sd] median   max
Connect:        3    3   0.1      3       3
Processing:   504  506   1.7    505     509
Waiting:      504  506   1.7    505     509
Total:        507  508   1.7    508     512

Percentage of the requests served within a certain time (ms)
  50%    508
  66%    509
  75%    509
  80%    511
  90%    512
  95%    512
  98%    512
  99%    512
 100%    512 (longest request)

o Adding +1 concurrency level (taking concurrency to 3), we produce a serializing bottleneck again:

USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
apache   30209  0.0  0.4  57132  8488 ?        S    15:30   0:00 /usr/bin/php-cgi
apache   30214  0.0  0.4  57132  8484 ?        S    15:30   0:00 /usr/bin/php-cgi
apache   31866  1.2  0.4  57132  8488 ?        S    15:34   0:00 /usr/bin/php-cgi

Concurrency Level:      3
Time taken for tests:   2.083 seconds
Complete requests:      10
Failed requests:        0
Write errors:           0
Total transferred:      1560 bytes
HTML transferred:       0 bytes
Requests per second:    4.80 [#/sec] (mean)
Time per request:       625.025 [ms] (mean)
Time per request:       208.342 [ms] (mean, across all concurrent requests)
Transfer rate:          0.73 [Kbytes/sec] received

Connection Times (ms)
              min  mean[+/-sd] median   max
Connect:        3    3   0.2      3       3
Processing:   504  612 337.9    505    1573
Waiting:      504  612 337.9    505    1573
Total:        507  615 337.9    508    1576

Percentage of the requests served within a certain time (ms)
  50%    508
  66%    508
  75%    508
  80%    509
  90%   1576
  95%   1576
  98%   1576
  99%   1576
 100%   1576 (longest request)

o And again, at 3 concurrency since 3 already spun up processes, no bottleneck:

USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
apache   30209  0.0  0.4  57132  8488 ?        S    15:30   0:00 /usr/bin/php-cgi
apache   30214  0.0  0.4  57132  8484 ?        S    15:30   0:00 /usr/bin/php-cgi
apache   31866  1.2  0.4  57132  8488 ?        S    15:34   0:00 /usr/bin/php-cgi


Concurrency Level:      3
Time taken for tests:   2.032 seconds
Complete requests:      10
Failed requests:        0
Write errors:           0
Total transferred:      1716 bytes
HTML transferred:       0 bytes
Requests per second:    4.92 [#/sec] (mean)
Time per request:       609.480 [ms] (mean)
Time per request:       203.160 [ms] (mean, across all concurrent requests)
Transfer rate:          0.82 [Kbytes/sec] received

Connection Times (ms)
              min  mean[+/-sd] median   max
Connect:        3    3   0.2      3       3
Processing:   504  505   0.5    505     506
Waiting:      504  505   0.5    505     506
Total:        507  508   0.5    508     508

Percentage of the requests served within a certain time (ms)
  50%    508
  66%    508
  75%    508
  80%    508
  90%    508
  95%    508
  98%    508
  99%    508
 100%    508 (longest request)