Windows server running APACHE crashing - CPU 100%

Hi
I’ve been having a major issue with my Drupal website for the past couple of weeks. I’ve been trying to home in on where the issue is coming from but at the moment it has been hard to work out if it is module related or server related.

Essentially my server is hitting 100% CPU and doesn’t stop until I reset APACHE. I’m not getting the WSOD with a PHP error and there are no new entries in my PHP error log. Also, because PHP doesn’t give me an error I haven’t been able to use xhprof to debug.

I found that this would happen when I had multiple users browsing the website and also when I quickly opened multiple tabs in my browser. I had at first thought it was because I had some views embedded in a page using the views field module, each of which I had contextual filters enabled. These pages were usually where the issue would arise.

I have however been able to replicate the crash by quickly opening pages in multiple tabs where views aren’t present. This then started to make me think it was server related, but because I don’t have much experience in the server side of things I wasn’t sure what to look for or how to debug.

The details of my server and module setup are below. I’d appreciate any help or direction on this as it’s become a show stopper as far as launching our site is concerned.

Server:Windows server 2012 – Intel Xeon 2.2GHz, 8GB RAM, 64-bit Operating System
APACHE: Apache/2.2.25
PHP: php-5.4.20-Win32-VC9-x86 - Memory limit 120M
Database: Microsoft SQL Server 10.50.1600 (using sqlsrv module) located in a different server
Drupal: 7.23
Memcache: 3.0.7
Modules that I thought could be linked to the issue (but might not be): views, entity reference, views field

The APACHE error log has the following entries when I replicate the crash:

[Wed Mar 12 18:46:37 2014] [notice] Parent: child process exited with status 255 -- Restarting.
[Wed Mar 12 18:46:37 2014] [notice] Apache/2.2.25 (Win32) PHP/5.4.20 configured -- resuming normal operations
[Wed Mar 12 18:46:37 2014] [notice] Server built: Jun 29 2013 19:23:21
[Wed Mar 12 18:46:37 2014] [notice] Parent: Created child process 5084
[Wed Mar 12 18:46:37 2014] [notice] Child 5084: Child process is running
[Wed Mar 12 18:46:37 2014] [notice] Child 5084: Acquired the start mutex.
[Wed Mar 12 18:46:37 2014] [notice] Child 5084: Starting 150 worker threads.
[Wed Mar 12 18:46:37 2014] [notice] Child 5084: Starting thread to listen on port 80.
[Wed Mar 12 18:46:37 2014] [notice] Child 5084: Starting thread to listen on port 80.
[Wed Mar 12 18:46:41 2014] [notice] Parent: child process exited with status 255 -- Restarting.
[Wed Mar 12 18:46:41 2014] [notice] Apache/2.2.25 (Win32) PHP/5.4.20 configured -- resuming normal operations
[Wed Mar 12 18:46:41 2014] [notice] Server built: Jun 29 2013 19:23:21
[Wed Mar 12 18:46:41 2014] [notice] Parent: Created child process 1628
[Wed Mar 12 18:46:41 2014] [notice] Child 1628: Child process is running
[Wed Mar 12 18:46:41 2014] [notice] Child 1628: Acquired the start mutex.
[Wed Mar 12 18:46:41 2014] [notice] Child 1628: Starting 150 worker threads.
[Wed Mar 12 18:46:41 2014] [notice] Child 1628: Starting thread to listen on port 80.
[Wed Mar 12 18:46:41 2014] [notice] Child 1628: Starting thread to listen on port 80.
[Wed Mar 12 18:51:33 2014] [notice] Parent: Received shutdown signal -- Shutting down the server.
[Wed Mar 12 18:51:35 2014] [notice] Child 1628: Exit event signaled. Child process is ending.
[Wed Mar 12 18:51:36 2014] [notice] Child 1628: Released the start mutex
[Wed Mar 12 18:51:53 2014] [notice] Parent: Child process exited successfully.

The windows evernt log has the following:

Faulting application name: httpd.exe, version: 2.2.25.0, time stamp: 0x51cf187f
Faulting module name: php5ts.dll, version: 5.4.20.0, time stamp: 0x523a144e
Exception code: 0xc0000005
Fault offset: 0x0004b4dd
Faulting process id: 0x65c
Faulting application start time: 0x01cf3e2368a98606
Faulting application path: C:\Apache2\bin\httpd.exe
Faulting module path: C:\php-5.4.20-Win32-VC9-x86\php5ts.dll
Report Id: a868e8ac-aa16-11e3-93f4-0050568b2e3b
Faulting package full name:
Faulting package-relative application ID:

Sorry about the amount of writing but I wanted to make sure I explained as much as I could.

Thanks

Nathan