Drupal Caching best practices and performance monitoring

Caching dos and don’ts

Best practices for long-term success

Do: Use granular tags

Target specific nodes (node:123) or fields (field:price) instead of broad tags like content_type:article. This prevents unnecessary cache clears.

Do: Implement multi-layer Caching

Combine different cache backends for speed and resilience. For example:
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// In settings.php (requires contrib modules)
$settings['cache']['bins']['page'] = 'cache.backend.chainedfast'; // Provided by Chained Fast Backend module
$settings['cache']['bins']['dynamic_page_cache'] = 'cache.backend.redis'; // Redis for shared cache

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Note: cache.backend.chainedfast is not in Drupal core. Learn more about Chained Fast Backend.

Do: monitor performance continuously

Instrument your code to log cache metrics:
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class CachePerformanceMonitor {
  public function collectPerformanceMetrics() {
    $metrics = [
      'cache_hit_ratio' => $this->calculateCacheHitRatio(),
      'avg_generation_time' => $this->getAverageCacheGenerationTime(),
    ];
    \Drupal::logger('cache_stats')->info('Performance Metrics: @metrics', ['@metrics' => print_r($metrics, TRUE)]);
    return $metrics;
  }
}

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Don’t: Cache sensitive data

Never cache CSRF tokens, user sessions, or personal information. Use cache contexts like user.roles to safely vary cache for different users.

Don’t: Over-Cache dynamic content

If your stock ticker updates every 10 seconds, don’t cache it with static content. Use max-age: 0 for rapidly changing data.

Debugging techniques

Diagnosing Cache issues

When your cache isn’t behaving, debugging is your lifeline. Let’s walk through a common scenario: a product detail page isn’t updating after inventory changes.

Step 1: Trace Cache lifecycle

Here’s a simple class to help you debug cache hits and misses:
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use Drupal\Core\Cache\CacheBackendInterface;

class CacheDebugger {
  public function traceCacheLifecycle($cache_id, $callback) {
    $cached = \Drupal::cache()->get($cache_id);
    if ($cached) {
      \Drupal::logger('cache_debug')->debug(Cache Hit: $cache_id);
      return $cached->data;
    }
    $data = $callback();
    // Set permanent cache, add a debug tag
    \Drupal::cache()->set($cache_id, $data, CacheBackendInterface::CACHE_PERMANENT, ['debug_trace']);
    \Drupal::logger('cache_debug')->warning(Cache Miss: $cache_id);
    return $data;
  }
}

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Step 2: Analyse Metadata

Check cache headers to see if your cache tags are working:
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curl -I https://example.com/node/123 | grep 'X-Drupal-Cache'

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If node:123 is missing from the tags, the cache won’t clear when the node updates.

Performance optimization checklist

A Practical audit guide

1. Cache Backend evaluation

• Are you still using the database for all caches?
• Is Redis powering your cache. render bin?
• Can your backend handle 10x the current traffic?

2. Caching strategy review

• Are you combining memory, Redis, and database tiers?
• Do you use cache contexts (like url.path) for more precise caching?
• Are critical systems (like search and user profiles) isolated in their own bins?

3. Invalidation analysis

• Do you use granular tags like node:123?
• Are related entities invalidated together (e.g., updating a category clears its products)?
• Are you avoiding unnecessary clears like cache_all on every config change?

4. Monitoring setup

• Are you logging cache hits and misses?
• Are slow-to-regenerate caches flagged for optimisation?
• Are you auditing tag usage to prevent over-invalidation?

Real-world implementation strategies

A phased approach

Phase 1: Assessment

• Benchmark: Use the Devel module to track SQL queries and render time.
• Identify bottlenecks: Are field formatters slowing down nodes?
• Current state: Is Redis in use, or is everything in the database?

Phase 2: Design

• Select backends: Redis for cache. render, APCu for cache, dynamic_page_cache.
• Tag strategy: Define tags like node:123, field: price, ml_model:42 for precise invalidation.
• Isolation plan: Move user profiles to their own cache bin to prevent interference.

Phase 3: Implementation

• Incremental rollout: Start with view modes, then add field-level caching.
• Monitor impact: Track metrics before and after each change.
• Adjust: If a bin causes memory bloat, switch from APCu to Redis.

Phase 4: Continuous Optimisation

• Fine-Tune: Adjust max-age based on how often data changes.
• Advanced techniques: Use cache locks to prevent stampedes on high-traffic pages.
• Iterate: Regularly audit and refine your strategy.

Case Study: Government education portal

Before optimisation, the portal’s pages took 4.2s to load due to untagged field formatters. After:

• Field-level caching reduced redundant processing.
• Redis-powered render cache cuts generation time.
• Granular tags ensured instant updates without over-clearing.

Series conclusion

From theory to practice

Throughout this 10-part series, we’ve explored the full spectrum of Drupal caching:

1. Fundamentals: Entity load caching, render arrays, and view modes.
2. Advanced techniques: Custom services, cache bins, dynamic contexts.
3. Optimisation: Tag management, stampede prevention, performance monitoring.

Caching isn’t a one-time task-it’s an ongoing process, like a chef adjusting seasoning based on taste. You must adapt your caching strategy as your site and audience evolve.

The government portal’s 93% speed improvement wasn’t magic-it was the result of layering caching mechanisms, intelligently invalidating stale data, and continuously monitoring performance. You can do the same!

Series navigation

This article is part of our comprehensive 10-part series on Drupal caching:

1. Introduction to Drupal Caching
2. Understanding Drupal’s Cache API
3. Choosing the Right Cache Backend for Your Drupal Site
4. Mastering Page and Block Caching in Drupal
5. Optimising Drupal Views and Forms with Caching
6. Entity and Render Caching for Drupal Performance
7. Building Custom Caching Services in Drupal
8. Implementing Custom Cache Bins for Specialised Needs
9. Advanced Drupal Cache Techniques‍
10. Drupal Caching Best Practices and Performance Monitoring (You are here)

What’s next?

Now that you’ve mastered caching, it’s time to put it into action! Start with your most visited pages, implement Redis for render arrays, or create a custom cache bin for an external API.

Remember: caching is a journey, not a destination. Stay curious, keep testing, and let performance be your compass.

Further Reading:

• Drupal Cache API Overview
• Cache Tags
• Cache Contexts
• Cache Backends
• Performance Monitoring
• Lock API

Caching is like a well-organised library: you don’t search every book for information-you use the catalogue to find exactly what you need. In Drupal, cache tags and contexts are your catalogue. Use them wisely, and your site will always be fast, fresh, and reliable.
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