Understanding Drupal's Internal Page Cache Module

A recent blog post by Luis Ruiz, Senior Drupal Developer at Metadrop, goes deep into the Internal Page Cache module, a critical Drupal feature designed to boost anonymous users' site performance. It basically means that when a page is cached, any request coming from an anonymous user can bypass the rendering and page building and directly get a fully rendered page from the cache. This caching system accelerates the load times but works only for anonymous users since pages served to authenticated users commonly consist of personalized elements not allow uniform caching.

Luis explains the technical workings of the module, detailing how cached pages are stored in the page_cache table, with key columns such as CID (unique identifier), TAGS (cache tags for invalidation), and EXPIRE (expiration settings). The blog also touches on HTTP middleware, which helps manage cached responses. For site admins curious about whether a page is cached, the post describes checking the X-Drupal-Cache header, which shows whether a cache "HIT" or "MISS" has occurred.

This module is critical for managers of small to medium-sized Drupal sites. As Luis advises, however, larger sites or high-traffic sites have other layers of caching that must be used instead of, or in addition to, the Internal Page Cache.