Adventures with WP-Cache2 & APC

Update 3: see update 2 for the solution!

APC (Alternative PHP Cache) is great for WordPress. It caches the compiled WordPress PHP files and greatly speeds up subsequent loads. I even wrote a WordPress plugin to make WordPress store its objects in APC instead of in the default file-based object cache.

WP-Cache2 is also great for WordPress, because it caches the HTML output of WordPress for a specified period.

So if both are good, together they should be awesome, right? Well… in theory, yes. Unfortunately, I’ve been having a heck of a time getting them to play together. What would happen was that pages would start showing up blank. Just a white page. Real helpful. The same thing happened when you tried to access /wp-admin/ The only way to fix it was to delete WP-Cache2. In desperation, I removed all the error-silencing @ from WP-Cache2. Ah. It was some problem with class_exists() and APC. Apparently, APC doesn’t play well with class_exists().

Here is the solution I came up with… it seems to be working. I’ve been able to enable/disable WP-Cache2, restart Apache2, flush APC, with no White Page of Death so far!

[ I have removed my solution, to keep from misleading people, as it gave me problems later on ]

Restart Apache, flush your WP-Cache2 cache, and cross your fingers. I’ll update if I have any problems with this.

Update: Well that was short-lived! I’m still looking for a solution. It may involve naming the wp-cache-config.php file differently for each WP install that is running WP-Cache2.

Update 2 (SOLUTION): This seems promising. In php.ini in the [apc] section I set apc.filters = wp-cache-config which should exclude wp-cache-config.php and wp-cache-config-sample.php from being cached by APC.

Update 3: Yep! That did it!

289 thoughts on “Adventures with WP-Cache2 & APC

  1. Good luck with this =). I will be keeping an eye out to see what you come up with and I just hope that there is a solution that doesn’t require access to php.ini (although I know some php.ini settings can be changed from within a script itself, kind of like how .htaccess can change httpd.conf settings).

  2. Same configuration, almost the same problem. I did this:

    apc.filters = “-.*cache.*\.php”, “podpress\.php”;

    podpress wasn’t working for me…

  3. Aha. That’s what I needed. I was just trying to install APC today, and ran into the blank-page problem. Filtering out wp-cache-config seems to have things working. I wonder why it conflicts like that?

  4. WP-Cache2 declares a class conditionally… and apparently APC doesn’t do well under those circumstances. I believe the error was due to the class not existing, because APC thought it didn’t when it should have. Blank page because errors are all turned off and everything is @silenced. I experimented with all sorts of things to make it work, but with no luck. This might change as APC matures… I hear it is under consideration for PHP6, but for now, filtering out wp-cache-config is a viable workaround.

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  6. How about something like PHPA which is also free and has gotten good reviews.

    It’s supposedly better than zend and yahoo uses it.
    Works with php 4.4.1 too.

    I don’t have it (or root) on my current host or I’d try it, but I’ve had it on previous hosts and it’s transparent.

  7. I am running the latest APC and WP-Cache and I’m getting the ‘white page of death’ error. I have tried a variety of filter settings in apc, flushing the wp-cache, and restarting apache. No luck yet. Mark – do you have WP-Cache successfully working with APC? As of now, I’m just going to use APC.

    Any other suggestions?

  8. Unfortunately, no luck here as well. Just as Ben’s problem; blank screen on first load, but subsequent loads work. I have removed all error suppressions from all wp-cache files. Even my log files are completely clean (after a couple file_exists() additions to the code. I’m still troubleshooting though…

  9. Solution has been discovered! I have posted the solution on my blog for details, but so you know I’m not link spammin ya, here’s how: Edit wp-cache-phase2 list 219. Change ob_end_clean() ob_end_flush().

    The problem is ob_end_clean() cleans out the buffer without actually flushing it to the screen and I don’t see any flush() calls before hand. Changing it to ob_end_flush() will end the output buffer and flush all data to standard out.

    I have tested this solution with and without APC and it seems to be working.

  10. Hi there,

    I was new to wordpress and those plugin staff. I had install this wp-cache plugin. I had enable the plugin from the optioin there.

    So how can i know that this plugin had take effect and how can i view the statistic thing?

    Anyhting to be check and any setting needed?



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  12. I am sorry for breaking WP-Cache/WP-Cache2 with APC … with a decent enough test case, that bug was fixed for good today (for php4, php5 having had that fix for months).

  13. I just found this. Interesting article as I am setting up a multi-server architecture for something unrelated to blogging and was investigation PHP opcode cache, APC and eAccelerator.

    I plan to host my own blog on my own server in a colo soon (in the near future) so I will let you know how it goes.

  14. was new to wordpress and those plugin staff. I had install this wp-cache plugin. I had enable the plugin from the optioin there.

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  16. How did you track down the error to that one file? I’ve got a server with APC which is serving blank white pages (with 500 status), but there’s nothing in the PHP or Apache error logs… most frustrating.

  17. I’m having the blank-page problem with WordPress 2.8.4 + APC without the WP-Cache2 plugin, does anoy one else had this problem before?
    What is odd, is that the blank pages just come from time to time, what I mean is the blog is working right now, but at any time it stars to serv blank pages, and then fix it by it self!

    1. Im am currently having that problem too. I just upgraded to APC 3.1.3p1 and PHP 5.2.11

      I am getting blank pages when I go to the admin area on all my installations.

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  25. There is a more straightforward and general solution to eliminating the WordPress white screen of death issue when using APC Cache

    Since the problem appears to reside with include file(s)
    Set apc.include_once_override=0 in your /etc/php5/conf,d/apc.ini file


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