Introduction

Definition

It is a data storage layer that stores the results of operations so that when they are required again, there is no need to redo them.

Why perform an operation more than once if the result is the same?

Benefits

Why is so important in Drupal

PHP and Drupal

PHP

• OPcache extensions.
• Store compiled PHP script in shared memory.
• It is essential for any Drupal site to improve performance.

• It is used to cache data in memory.

Drupal Cache System

Cache backend

Cache bin

Cache bin defined in core.services.yml

  cache.config:
  class: Drupal\Core\Cache\CacheBackendInterface
  tags:
    - { name: cache.bin, default_backend: cache.backend.chainedfast }
  factory: ['@cache_factory', 'get']
  arguments: [config]

  cache.entity:
  class: Drupal\Core\Cache\CacheBackendInterface
  tags:
    - { name: cache.bin }
  factory: ['@cache_factory', 'get']
  arguments: [entity]

Cache bin examples

• cache.bootstrap: stores necessary information for Drupal's execution that varies very little.
• cache.config: configuration and configuration entities.
• cache.entity: Stores the values of existing content entities in Drupal.
• cache.render: contains cached HTML strings like cached blocks, which can grow to large sizes.

Cache objects dependencies

Cache metadata examples

Cache invalidation

Interaction with the Cache API

Directly

Interacting directly with the Cache API of Drupal, taking care of caching objects, retrieval, and invalidation ourselves.

  
   $cid = 'my_module_example:' . \Drupal::languageManager()
    ->getCurrentLanguage()->getId();
   $data = NULL;
   if ($cache = \Drupal::cache()->get($cid)) {
     $data = $cache->data;
   }
   else {
     $data = my_module_complicated_calculation();
     \Drupal::cache()->set($cid, $data);
   }
  

Interaction with the Cache API

Indirectly

Indirectly through the Render API. This second system is the most common.

  
  $renderer = \Drupal::service('renderer');
  $config = \Drupal::config('system.site');
  $current_user = \Drupal::currentUser();
  $build = [
    '#markup' => t('Hi, %name, welcome back to @site!', [
      '%name' => $current_user->getUsername(),
      '@site' => $config->get('name'),
    ]),
    '#cache' => [
      'contexts' => [
        'user',
      ],
    ],
  ];

  $renderer->addCacheableDependency($build, $config);
  $user_entity = \Drupal\user\Entity\User::load($current_user->id());
  $renderer->addCacheableDependency($build, $user_entity);
  

Cache Dependency Propagation

The dependencies defined in the different components are propagated to their ancestors for the invalidation to be effective.

Response caching

How does Dynamic Page Cache work?

It caches response objects with dynamic components by replacing those components with placeholders.

It waits until the last moment to render those components and replace the placeholders.

External Caching System

Module Purge

purge_purger_httptc, purge_queuer_url, acquia_purge, akamai, cloudflare, cloudfront_purger, fastlypurger, keycdn, varnish_purge, max_cdn_cache, Nginx_cache_clear, purge_file

Response headers

Why are response headers useful:

• To send configuration about caching to other systems, for example, Browser, CDN, etc. (Max Age, Cache tags).
• For us, to debug.

Types of headers:

• Standard HTTP headers.
• Not standard HTTP headers prefixed with “X-” or another prefix, like “cf-”, added by Drupal and other cache layers.

Debugging Drupal headers

Cache Review