Digitaldogma

FastCGI + PHP

I run this webserver on a VPS hosted by quantact so the lower the memory usage, the
lower my monthly bill. This has led me to be pretty stingy with memory usage.
While using mod_php, each apache process was around 25MB each. Since switching
to PHP running as a fastcgi my apache processes are down to around 2MB with a
couple of php process at around 25MB.

Configuration

I followed these instructions to set everything up. The only real gotcha’s I ran into were
ensuring the file permissions were correct as php is now running as a different
user that www-data.

Benchmarks

I use ab to beat on the server a bit in both configurations, below are the results for mod_php:

Server Software:        Apache/2.2.9
Server Hostname:        www.digitaldogma.org
Server Port:            80

Document Path:          /2010/10/09/monitoring-with-cacti
Document Length:        20745 bytes

Concurrency Level:      25
Time taken for tests:   45.775 seconds
Complete requests:      1000
Failed requests:        229
   (Connect: 0, Receive: 0, Length: 229, Exceptions: 0)
Write errors:           0
Non-2xx responses:      96
Total transferred:      17081694 bytes
HTML transferred:       16537051 bytes
Requests per second:    21.85 [#/sec] (mean)
Time per request:       1144.374 [ms] (mean)
Time per request:       45.775 [ms] (mean, across all concurrent requests)
Transfer rate:          364.42 [Kbytes/sec] received

Connection Times (ms)
              min  mean[+/-sd] median   max
Connect:       74   82   4.6     81     107
Processing:    80 1048 746.3    936    8988
Waiting:       80  863 586.0    757    6633
Total:        163 1131 746.0   1019    9069

Percentage of the requests served within a certain time (ms)
  50%   1019
  66%   1185
  75%   1299
  80%   1384
  90%   1734
  95%   2181
  98%   3174
  99%   3940
 100%   9069 (longest request)

and for FastCGI:

Server Software:        Apache/2.2.9
Server Hostname:        www.digitaldogma.org
Server Port:            80

Document Path:          /2010/10/09/monitoring-with-cacti
Document Length:        20745 bytes

Concurrency Level:      25
Time taken for tests:   52.335 seconds
Complete requests:      1000
Failed requests:        0
Write errors:           0
Total transferred:      21287344 bytes
HTML transferred:       20748806 bytes
Requests per second:    19.11 [#/sec] (mean)
Time per request:       1308.374 [ms] (mean)
Time per request:       52.335 [ms] (mean, across all concurrent requests)
Transfer rate:          397.22 [Kbytes/sec] received

Connection Times (ms)
              min  mean[+/-sd] median   max
Connect:       74   82   4.9     81     123
Processing:   316 1201 234.2   1136    2588
Waiting:      155 1025 232.3    960    2408
Total:        398 1283 234.4   1219    2667

Percentage of the requests served within a certain time (ms)
  50%   1219
  66%   1317
  75%   1401
  80%   1469
  90%   1577
  95%   1710
  98%   1928
  99%   2103
 100%   2667 (longest request)

When I first looked at the results, it appears that the mod_php config was faster based on the Time per request, but then I noticed the Failed requests numbers. Of the 1000 requests, 229 had failed on the mod_php server, looking in the error logs I find quite a few of these:

[error] (12)Cannot allocate memory: fork: Unable to fork new process

Looks like the mod_php exhausted the system memory and wasn’t able to process all the requests. This would account for the faster response times, as it doesn’t take much to reply with an error :).

The above has cemented my decision to go with FastCGI on my hosted VPN. If you are able to throw more memory at it I get the feeling mod_php would be faster (note the max connect times, as the first hit need to spawn the fastcgi process), but for my small site and limited resources (money and ram :) FastCGI is the way to go.