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I have a server running very slowly due to high CPU usage. I think this must be a configuration issue but I can't put my finger on why. The server is running Plesk and I've configured PHP to run as a Fast CGi application.

Server spec:

Quad-Core AMD 2.2GHz 4GB RAM Ubuntu 10.04 Apache 2.2.14 PHP 5.3.2

Websites:

1 x Drupal 7 2 x WordPress 3.x

Apache config:

KeepAlive On Timeout 30 MaxKeepAliveRequests 0 KeepAliveTimeout 2 <IfModule mpm_prefork_module> StartServers 4 MinSpareServers 5 MaxSpareServers 10 MaxClients 20 MaxRequestsPerChild 5000 </IfModule>

Notice the high CPU

I have APC enabled plus the Drupal site has all caching turned on, including caching in views. I have another server running over 100 sites on CentOS and cpu usage is very low. Any ideas what could be causing this?

Heres a mod_status output screenshot

enter image description here

Also there is no output in the apache error.log apart from MaxClients being exceeded.

top CPU and Memory lines added 25th Apr enter image description here

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    How much available RAM do you have? ( free -h ) , each php5-cgi process is consuming about 100 MB (which seems 3x on the high side) so try: a) increasing MaxClients according to available RAM b) unload unneeded modules c) if still high CPU, reduce TimeOut, take out KeepAlive Commented Apr 22, 2014 at 16:02
  • Are you sure you mean prefork, and not mpm_worker with mod_fcgid? I believe if you use prefork, you shouldn't see php5-cgi processes in your process list, but apache2-processes. If you visit the websites on the affected server, how do you rate the performance? Are they slow to respond, or just as fast as other websites? Commented Apr 22, 2014 at 22:01
  • 4GB RAM (1.6GB Free). In plesk I've switched from fcgi to apache module several times to test things each time they are still affected by the prefork config. I've taken out keep alive and put max clients down to 10 which has taken CPU down to about 80% but sites are slow as hell Commented Apr 23, 2014 at 10:51
  • What server MPM is listed when you set fcgi and run apache2ctl -V? And what if you use 'apache module'? Commented Apr 23, 2014 at 13:57
  • server/mpm/prefork, In plesk you can set fcgi/apache per domain so one can be fcgi while another apache module, with all set to apache module apache2ctl -V is still prefork Commented Apr 23, 2014 at 14:10

2 Answers 2

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No amount of Apache or PHP tuning will help you, it's time to see what makes Drupal or Wordpress so slow. I guess you have some custom modules in one or both of them and some custom module is dragging the performance down. Try disabling custom modules one by one and see if that helps. Also enable logging in your database and spot the slow and/or excessive queries.

When it comes to Drupal, Boost can be an excellent performance boost. With WordPress, W3TC tends to help a lot.

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  • You are right they do have a lot of customisations. I've disabled what I can but I guess this could be a lesson to teams that push deadlines so much that quality of code is affected, always has repercussions. Commented Apr 29, 2014 at 8:34
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My problem is now fixed, below is the steps I took.

  • Migrated server to Ubuntu 14 LTS with latest software including PHP 5.5
  • Split MySQL load on to its own server instance
  • Uninstalled Drupal modules that weren't needed

Note: None of the above fixed my CPU issue

Added Honeypot from http://www.projecthoneypot.org/ and BOOM, CPU load reduced to under 10%. So my issue was down to HTTP spam coming in at over 5 requests per second (400,000 per day) on a page with heavy SQL queries but one problem does remain... My site does NOT appear to scale well, I guess if this was legitimate traffic I'd have to look at optimising / caching wherever possible as Janne suggested.

Thanks to everyone for their advice.

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