As of December 1st, 2015 the PHP APC extension will no longer be supported by ZenCache. If you arrived at this page from a ZenCache notice about the APC Extension, you will need to disable APC in your wp-config.php as described below, or contact your web hosting company and request that your server be switched to the PHP OPCache extension, or that your server be upgraded to PHP 5.5 or higher (APC has been replaced with OPCache starting with PHP 5.5).

Note that recommends running PHP 5.6, so if you're currently running an older version of PHP, you may want to take this opportunity to contact your web hosting company and request that your server be updated.

Why is ZenCache no longer supporting the APC extension?

The PHP APC extension is an outdated and buggy extension (the last update to the APC extension was 2012) and the PHP community has since abandoned development of the APC extension in favor of the newer OPCache extension. We discovered several major issues with the APC extension that were resulting in fatal errors on some of our users sites who were running the newer ZenCache Pro codebase. In July 2015 we began showing an APC Extension Warning whenever ZenCache Pro detected that the APC extension was being used.

As part of increasing the minimum required PHP version for ZenCache to PHP 5.4 (see New Minimum PHP Version: PHP 5.4), we are also completely deprecating the support for the APC extension.

How do I disable PHP APC?

To disable PHP APC, you can add ini_set('apc.cache_by_default', false); to the top of your /wp-config.php file. That will allow future versions of ZenCache to run (as long you're also running PHP 5.4+; see New Minimum PHP Version: PHP 5.4).

However, some web hosting companies do not allow you to disable PHP settings using the ini_set() function, so if adding the above line to your wp-config.php file does not disable PHP APC, you will need to contact your web hosting company.

How do I switch to the PHP OPCache extension?

The PHP OPcache extension, which replaces the outdated APC extension, is software that runs on your website's server, so you'll most likely need to contact your web hosting company and ask them to make this change. (Since the APC extension is no longer used at all starting with PHP 5.5, we recommend simply requesting that your web host upgrade PHP on your server to PHP 5.5+).

Here's a letter that you can send your web hosting company:

Dear web host,

I'm running a WordPress website on one of your servers and one of the plugins (ZenCache) requires that the outdated and buggy PHP APC extension be disabled in favor of the PHP OPcache extension. Upgrading my server to PHP 5.5 or higher would also solve this issue, as the APC extension is no longer used after PHP 5.5. WordPress, the CMS that ZenCache runs on, has listed PHP 5.6 as the recommended PHP version on their requirements page:

Can you please upgrade my hosting to PHP 5.5 or higher or simply replace the APC extension with OPcache?

I look forward to your reply.

What if I cannot switch to OPcache, upgrade to PHP 5.5, or disable the APC extension?

If your web hosting company does not support PHP 5.5 or higher, or if they're unwilling to disable the APC extension, we recommending finding a web host that does support PHP 5.5 or higher. All of the web hosts recommended by WordPress support PHP 5.6 or higher.