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Anti-Patterns & Common Mistakes

When to Use

When you need to avoid common caching mistakes that cause bugs, performance issues, or stale content.

Decision

Anti-pattern Why it's wrong Do this instead
Using Cache::PERMANENT without cache tags Content never invalidates when source changes Add cache tags for source data
Using user context for role-based content Creates per-user cache entries (huge cache) Use user.roles or user.permissions:{permission}
Manually copying cache metadata between arrays Renderer does this automatically via bubbling Let bubbling handle metadata propagation
Using deleteAll() to fix cache issues Clears valid entries, expensive operation Use targeted cache tag invalidation
Forgetting cache metadata on render arrays Serves stale content, incorrect variations Always set tags, contexts, max-age
Adding same tags on parent and child Unnecessary duplication, metadata bubbles Set tags on children only
Using per-request cache tags Tags not reusable, cache never hits Use reusable tags (entity ID, config name)
Storing objects in cache bins Serialization overhead, version incompatibility Store simple data structures
Not using DI for cache bins Static calls harder to test, less flexible Inject CacheBackendInterface via DI
Creating too many lazy builders Each placeholder adds overhead Use sparingly (2-5 per page)

Pattern

Wrong: Manual metadata copying 

// DON'T DO THIS
$child = ['#cache' => ['tags' => ['node:123']]];
$parent = [
  'child' => $child,
  '#cache' => ['tags' => ['node:123']],  // Duplicated, unnecessary
];

Right: Let bubbling handle it 

// DO THIS
$child = ['#cache' => ['tags' => ['node:123']]];
$parent = [
  'child' => $child,
  // Tags bubble automatically from child
];

Wrong: Clearing entire bin 

// DON'T DO THIS
\Drupal::cache('render')->deleteAll();  // Clears ALL render cache

Right: Targeted tag invalidation 

// DO THIS
\Drupal::service('cache_tags.invalidator')
  ->invalidateTags(['node:123']);  // Only clears affected entries

Wrong: Per-user context for role-based content 

// DON'T DO THIS
'contexts' => ['user']  // Separate cache per user

Right: Role-based context 

// DO THIS
'contexts' => ['user.roles']  // One cache per role combination

Reference: Common caching mistakes

Common Mistakes

  • Over-caching with Cache::PERMANENT — Causes stale content; use appropriate max-age or rely on tags
  • Under-caching with max-age 0 — Makes everything uncacheable; use placeholders for variable parts
  • Not understanding cache context cardinality — user context creates thousands of cache entries
  • Testing only as admin — Admin bypasses Page Cache and has different permissions; test as anonymous and authenticated

See Also