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Tom
Asked: 2012-05-25 08:38:01 +0800 CST

Incompatibility between WP super cache and PHP APC?

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I'm using the "WP super cache" WordPress plugin on a Ubuntu 12.04 server and found it is incompatible with php APC.

After installing and activating the WordPress plugin, the blog was down and users were getting a error page:

HTTP Error 500 (Internal Server Error): An unexpected condition was encountered while the server was attempting to fulfil the request.

I noticed a segmentation fault in the Apache error log (/var/log/apache2/error.log).

In the troubleshooting section of the WP super cache FAQ I noticed a description of my problem:

  1. The "white screen of death" or a blank page when you visit your site is almost always caused by a PHP error but it may also be caused by APC. Disable that PHP extension if you have trouble and replace with eAccelerator or Xcache.

So I commented out the apc Apache extension and restarted Apache:

> sudo emacs /etc/php5/apache2/conf.d/apc.ini 
;extension=apc.so
> sudo service apache2 restart

Sure enough, that fixed the problem - the blog was back up and caching enabled.

The thing is, I actually want APC cache to run as well. The opcode cache is useful. I know I could use another opcode cache but does anyone know a APC setting I can change to allow this plugin to work with APC?

Note: I also tried Ubuntu 10.10, 11.04, 11.10 and had exactly the same issue.

php

1 Answers

  1. Been looking around for some more technical explanation of this.

    I don't believe this problem is Ubuntu related. I've seen similar Wordpress WSOD crashes... APC, WP Supercache, Apache, FreeBSD. Site(s) would run reliably for some period of time then WSOD all of a sudden.

    Apache restart (which would flush APC cache in memory) fixed the issue.

    Turning off SuperCache fixes the issue.

    SuperCache probably has some obscure bug with APC...character encoding bug?

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