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Load testing a django 1.21/Apache/mod_wsgi configuration on an AWS small instance (Ubuntu 10.04) with Apache bench is showing extremely high CPU load (using uptime and vmstat) at low concurrent requests:

ab -c 5 -n 1000 "my_url"

...causes this uptime output:

18:04:54 up 9 days, 16:54,  3 users,  load average: 5.33, 2.45, 1.91

CPU is at 100% even with an Apache bench concurrency value of 2. I'm running Apache bench from a different AWS instance in the same region/zone. Ideas on what's the problem, or how I should continue to debug this?

Details:

  • Out of desperation, I installed a vanilla django project/app with a simple "Hello World" view (no DB calls, etc). Same results. So I doubt it's my application code.
  • Memory usage looks fine during the load test.

Here's a vmstat output before/during/after load test:

procs -----------memory---------- ---swap-- -----io---- -system-- ----cpu----
r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id wa
0  0      0 1034484  94848 321320    0    0     0     0   13   29  0  0 100  0
6  0      0 1032916  94848 321328    0    0     0     0  262  720  4 32 12  0
6  0      0 1031684  94848 321336    0    0     0     0  312  796  7 33  0  0
8  0      0 1030892  94856 321344    0    0     0    12  302  763  4 36  0  0
...
6  0      0 1030268  94864 321376    0    0     0     0  302  843  3 39  0  0
0  0      0 1032452  94868 321380    0    0     0    12  183  516  3 22 34  0
1  0      0 1033988  94868 321388    0    0     0     0   24   38  1  2 92  0
0  0      0 1033996  94868 321388    0    0     0     0   17   28  0  0 100  0
  • I'm running a prefork version of apache2 since I'm also running WordPress, which relies on PHP. (PHP doesn't play well with Apache worker version)

Here's my virtual hosts file:

WSGIPythonHome /home/xxx/webapps/ve/api
<VirtualHost *:80>
        ServerAdmin webmaster@localhost
        ServerName  app.xxx.mobi

        WSGIDaemonProcess snaplive user=www-data group=www-data processes=10 threads=1 maximum-requests=10000
        WSGIProcessGroup snaplive
        WSGIScriptAlias / /home/xxx/webapps/api/settings/apache/prod.wsgi
        DocumentRoot /home/xxx/webapps/api/static
        ErrorLog /var/log/apache2/django-live/error.log
        CustomLog /var/log/apache2/django-live/access.log combined
</VirtualHost>

Here's my httpd.conf file:

Alias /media /home/xxx/Django-1.2.1/django/contrib/admin/media
LoadModule headers_module /usr/lib/apache2/modules/mod_headers.so

StartServers 2
MinSpareServers 2
MaxSpareServers 5
MaxClients 50
MaxRequestsPerChild 3000
ServerLimit 8
Keepalive off
HostnameLookups Off

Here's my wsgi file:

import os
import sys
sys.stdout = sys.stderr

from django.core.handlers.wsgi import WSGIHandler
os.environ['DJANGO_SETTINGS_MODULE'] = 'settings'
application = WSGIHandler()

sys.path.append("/home/xxx/webapps/api")

By hitting a django url from a browser during the load test, I've confirmed qualitatively that the high CPU load is impacting performance.

I've read that this might not be important, but I'm seeing this a lot in my error logs:

[Sun Sep 19 18:04:58 2010] [error] Exception KeyError: KeyError(-1218693376,) in <module 'threading' from '/usr/lib/python2.6/threading.pyc'> ignored

Here are my Apache bench results, in case helpful:

Server Software:        Apache/2.2.14
Server Hostname:        app.xxx.mobi
Server Port:            80

Document Path:          /plist_catalog/test_data
Document Length:        0 bytes

Concurrency Level:      5
Time taken for tests:   27.720 seconds
Complete requests:      1000
Failed requests:        0
Write errors:           0
Non-2xx responses:      1000
Total transferred:      269000 bytes
HTML transferred:       0 bytes
Requests per second:    36.08 [#/sec] (mean)
Time per request:       138.598 [ms] (mean)
Time per request:       27.720 [ms] (mean, across all concurrent requests)
Transfer rate:          9.48 [Kbytes/sec] received

Connection Times (ms)
              min  mean[+/-sd] median   max
Connect:        1    2   8.5      1      88
Processing:     9  136 176.9     81    1182
Waiting:        9  135 176.6     81    1182
Total:         10  138 176.7     83    1183

Percentage of the requests served within a certain time (ms)
  50%     83
  66%     98
  75%    128
  80%    140
  90%    423
  95%    576
  98%    727
  99%    819
 100%   1183 (longest request)

2 Answers 2

2

The issue was that I had installed the package apache2-mpm-itk instead of apache2-mpm-prefork. apache2-mpm-itk is derived from apache2-mpm-prefork, but for some reason, didn't perform well when used with mod_wsgi.

1
  • When using ITK MPM and mod_wsgi, recommended to use mod_wsgi daemon mode and disable Python interpreter usage in embedded processes. If embedded mode is used then you are loading your application on every request just like CGI. Jul 28, 2011 at 23:56
0

My recent experience with django is that it consumes CPU like a hog. My app is fairly small but whenever i get concurrent requests (only 15 or more requests) django always takes up 80% - 100% of my CPU.

I later increased the CPU cores and the app started running fine.

BASIC ADVICE:

How much RAM does your server need?

    Minimum of 8Gig or more for medium sized apps.

How many CPU Cores does your server need?

    The number of cores that you will need within your server is directly related to the types of loads you plan to run on your server. 6 to 8 cores for medium sized apps.

More cores immediately translate into more performance under load.

How many IOPS does your server need?

The I/O usage refers to the disk input and output (I/O).Similarly IOPS refers to Inputs Outputs Per Second.
IOPS determines the speed at which a hard drive reads data from and writes data to a hard drive. 
A high quality Hitachi Ultrastar 15K600 15K SAS disk can deliver as many as 400 IOPS in server tasks, 
While a modern SSD disk can easily delivery 10,000 IOPS or more.

References:

https://www.eurovps.com/blog/how-much-ram-cpu-storage-iops-vps-needs

https://www.milesweb.com/hosting-faqs/all-you-need-to-know-about-web-hosting-i-o-usage-iops-limit-and-entry-processes-limit

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