Mark Jaquith

APC Object Cache provides a persistent memory-based backend for the WordPress object cache. APC must be available on your PHP install.
An object cache is a place for WordPress and WordPress extensions to store the results of complex operations. On subsequent loads, 
this data can be fetched from the cache, which will be must faster than dynamically generating it on every page load.
The APC Object Cache backend is also compatible with <a href="https://wordpress.org/extend/plugins/batcache/" rel="ugc">Batcache</a>, the powerful full page caching engine that runs on WordPress.com
Be sure to read the installation instructions, as this is not a traditional plugin, and needs to be installed in a specific location.

APC Object Cache Backend

APC Object Cache provides a persistent memory-based backend for the WordPress object cache. APC must be available on your PHP install.

Daniel Bachhuber

Pantheon Systems

stevector

For sites concerned with high traffic, speed for logged-in users, or dynamic pageloads, a high-speed and persistent object cache is a must. WP LCache improves upon Memcached and Redis object cache implementations by using APCu, PHP’s in-memory cache, in a way that’s compatible with multiple web nodes. Under the hood, WP LCache uses <a href="https://github.com/lcache/lcache" rel="nofollow ugc">LCache</a>, a library that applies the tiered caching model of multi-core processors (with local L1 and central L2 caches) to web applications.
Note: WP LCache development is currently on hold, and not recommendated for production use, due to an <a href="https://github.com/lcache/wp-lcache/issues/138" rel="nofollow ugc">issue with APCu cache fragmentation</a>. <a href="https://wordpress.org/plugins/wp-redis/" rel="ugc">WP Redis</a>, also maintained by Pantheon, is a great alternative.
WP LCache is faster than other object cache implementations because:
<ul>
<li>By using APCu, which is in-memory, WP LCache uses the fastest possible persistent object cache backend and avoids costly network connections on every request. When using a Memcached or Redis-based persistent object cache where Memcached or Redis is on a different machine, the millisecond cost of each cache hit can add up to seconds of network transactions on every request.</li>
<li>By incorporating a common L2 cache, WP LCache synchronizes cache data between multiple web nodes. Cache updates or deletes on one node are then applied to all other nodes. Without this synchronization behavior, APCu can’t be used in server configurations with multiple web nodes because the cache pool is local to the machine.</li>
</ul>
Still not convinced? WP LCache includes features that no one else has:
<ul>
<li>Cache groups are handled natively, meaning you can delete an entire group of keys with <code>wp_cache_delete_group()</code>.</li>
<li>WordPress’ alloptions cache is sharded into distinct keys, mitigating cache pollution on high traffic sites. <a href="https://core.trac.wordpress.org/ticket/31245" rel="nofollow ugc">Read #31245</a> for all of the gory details.</li>
</ul>
Read the installation instructions, then install WP LCache from <a href="https://wordpress.org/plugins/wp-lcache/" rel="ugc">WordPress.org</a> or <a href="https://github.com/lcache/wp-lcache" rel="nofollow ugc">Github</a>.
Go forth and make awesome! And, once you’ve built something great, <a href="https://github.com/lcache/wp-lcache/issues" rel="nofollow ugc">send us feature requests (or bug reports)</a>.
<h3>Contributing</h3>
The best way to contribute to the development of this plugin is by participating on the GitHub project:
https://github.com/lcache/wp-lcache
Pull requests and issues are welcome!
You may notice there are two sets of tests running, on two different services:
<ul>
<li>Travis CI runs the <a href="https://phpunit.de/" rel="nofollow ugc">PHPUnit</a> test suite in a variety of environment configurations (e.g. APCu available vs. APCu unavailable).</li>
<li>Circle CI runs the <a href="http://behat.org/" rel="nofollow ugc">Behat</a> test suite against a Pantheon site, to ensure the plugin’s compatibility with the Pantheon platform.</li>
</ul>
Both of these test suites can be run locally, with a varying amount of setup.
PHPUnit requires the <a href="https://make.wordpress.org/core/handbook/testing/automated-testing/phpunit/" rel="nofollow ugc">WordPress PHPUnit test suite</a>, and access to a database with name <code>wordpress_test</code>. If you haven’t already configured the test suite locally, you can run <code>bash bin/install-wp-tests.sh wordpress_test root '' localhost</code>. You’ll also need to install and configure APCu in order to run the test suite against APCu.
Behat requires a Pantheon site. Once you’ve created the site, you’ll need <a href="https://github.com/pantheon-systems/terminus#installation" rel="nofollow ugc">install Terminus</a>, and set the <code>TERMINUS_TOKEN</code>, <code>TERMINUS_SITE</code>, and <code>TERMINUS_ENV</code> environment variables. Then, you can run <code>./bin/behat-prepare.sh</code> to prepare the site for the test suite.

WP LCache

Supercharge your WP Object Cache with LCache, a persistent, performant, and multi-layer cache library.

APC Object Cache Backend vs WP LCache