Cache tags

“There are only two hard problems in Computer Science: cache invalidation and naming things.”

• Caching is easy
• Cache invalidation is hard
• Poor cache invalidation

  ⬇

  poor performance

  ⬇

  more servers

1. Cache invalidation is hard

… clears the entire page cache on node save!

Cache clearing in Drupal 7

1. Clear a specific cache entry:

   cache_clear_all('foo:content:id', $bin);

2. Clear a coarse set of cache entries:

   cache_clear_all('foo:content:', $bin, TRUE);

3. Clear all entries:

   cache_clear_all('*', $bin, TRUE);

Cache tags in Drupal 8

cache($bin)->set($cid, $value, CACHE_PERMANENT, $tags);

• Something in page cache:

  $tags = array('content' => TRUE);

• HTML containing title of node 42:

  $tags = array(
    'node' => array(42)
  );

• Node with two Taxonomy terms:

  $tags = array(
    'node' => array(42),
    'user' => array(314),
    'taxonomy_term' => array(1337, 9001),
  );

Using cache tags in render arrays

$element['#cache'] = array(
  'keys' => array('entity_view', $entity_type, $entity_id, $view_mode),
  'granularity' => DRUPAL_CACHE_PER_ROLE,
  'tags' => array(
    $entity_type . '_view' => TRUE,
    $entity_type => array($entity_id),
  ),
);

/**
 * Collects cache tags for an element and its children into 1 array.
 *
 * […] This allows items to be invalidated based on all tags attached
 * to the content they're constituted from.
 */
function drupal_render_collect_cache_tags($element) { … }

2. Caching is easy

Contextual links in Drupal 7

Contextual links: HTML in Drupal 7

  

    

      Bewerken
    
    

      Verwijderen
    
  

						

• Embedded in node's HTML
• Adapt to user's permissions + page

⟹ breaks render cache

Contextual links: HTML in Drupal 8

or

• Embedded in node's HTML
• Invisible placeholder!

⟹ compatible with render cache

Contextual links: logic in Drupal 8

Contextual IDs in HTML

Conclusion (cache tags)

Use cache tags precisely (cache invalidation)

• Tag render arrays
• Delete tags: prevent stale content
• Invalidate tags: allow stale content

Personalize via JS, cache client-side (cache filling)

• Cacheable render arrays
• Universal truths: data- attributes
• Personalization: JS + localStorage

Pluggable asset optimization

CSS/JS aggregation in Drupal 7

• JS minification: none
• Changing CSS/JS minifier: impossible
• Asset grouping: dumb
• Script loader: impossible
• …

CSS/JS aggregation in Drupal 7

“API”:

• #aggregate_callback
• #group_callback

CSS/JS aggregation in Drupal 8

API:

• More explicit
• More building blocks

Asset services

Override at will!

asset.css.collection_renderer:
  class: Drupal\Core\Asset\CssCollectionRenderer
asset.css.collection_optimizer:
  class: Drupal\Core\Asset\CssCollectionOptimizer
  arguments: [ '@asset.css.collection_grouper', '@asset.css.optimizer', '@asset.css.dumper', '@state' ]
asset.css.optimizer:
  class: Drupal\Core\Asset\CssOptimizer
asset.css.collection_grouper:
  class: Drupal\Core\Asset\CssCollectionGrouper
asset.css.dumper:
  class: Drupal\Core\Asset\AssetDumper
asset.js.collection_renderer:
  …
asset.js.collection_optimizer:
  …
asset.js.optimizer:
  …
asset.js.collection_grouper:
  …
asset.js.dumper:
  …

Asset services: possibilities

1. Asset dumper: external server (CDN, S3 …)
2. JS optimizer: UglifyJS
3. JS collection renderer: LabJS script loader
4. Groupers: 3rd party data mining ⇒ globally optimal groups
5. Collection optimizer:
   • new aggregate ⟺ changed mtime
   • use custom architecture entirely!

Conclusion (asset handling)

Override individual asset services

• Improve individual services (use existing architecture)
• Or apply your own architecture!