APCu Cache Basics
Understand APCu and its uses within the Pantheon WebOps workflow.
APCu is a user-accessible PHP cache. Pantheon provides APCu by default across all plans, but the size of the APCu memory cache (apc.shm_size) varies depending on the service level. See the Application Containers overview to learn more about APCu on Pantheon's container architecture.
Frequently Asked Questions
Can APCu be used as a cache backend on Pantheon?
Yes, APCu can be used as a cache backend or a "key-value store"; however, this is not recommended. APCu lacks the ability to span multiple application containers. Instead, Pantheon provides a Redis-based Object Cache as a caching backend for Drupal and WordPress, which has coherence across multiple application containers.
How can I determine what my current APCu settings are?
The shm_size is determined by the site plan. Sandbox sites and Basic site plans have a shm_size of 128 MB. Performance site plans and higher have a shm_size of 256 MB. These values can be seen in phpinfo.
Does "Clear Caches" Affect ACPu
No. The Clear Caches button in the Site Dashboard does not interact with APCu. The function apcu_clear_cache will clear the APCu cache for a single application container.