Cache Lifecycle in Drupal 9

22 / May / 2023 by sagar.verma 0 comments

Cache Life cycle is important to understand as it plays an important role in optimising the performance and scalability of web applications. In this blog, I will dive deep into the cache life cycle in Drupal 9, exploring its key stages and highlighting best practices to maximise caching benefits. Various Stages are as follows :-

  1. Cache Storage:
    At this stage, Drupal stores the generated content or data inside the cache storage backend, such as the database or a caching system like Redis or Memcached (i.e. explicit cache technique). The cache storage is typically used to store various types of data, including rendered HTML, configuration, database query results, and more. Additionally, Drupal defines cache bins as logical storage containers for cached data. Each cache bin can have its own configuration settings, allowing us to fine-tune caching behaviour for different components.
    Example: If our site has a frequently updated blog section. By configuring a separate cache bin for the blog content, we can control the caching behavior specifically for blog pages. We may set a lower cache expiration time for the blog cache bin to ensure that new blog posts are displayed promptly.
  2. Cache Retrieval: When a page or a component is requested, Drupal checks if a valid cached version is available. If a valid cache entry is found, Drupal retrieves the cached data from the cache storage instead of regenerating it. This significantly improves the response time and reduces the load on the server.
  3. Cache Metadata: Each cache entry in Drupal is associated with cache metadata, which includes cache tags, cache contexts, and cache max-age. Cache tags identify the entities or elements that affect the cached content, cache contexts define the variations in the cached content based on contextual information, and cache max-age specifies how long the cache entry is considered valid.

    Let us understand this in detail:

    Cache Tags: Cache tags are a type of strings. They allow Drupal to invalidate related cache entries when changes occur efficiently. For example, when a node is updated, Drupal invalidates cache entries associated with that node’s cache tag, ensuring that the updated content is delivered.
    Example: Suppose in our site we have a product catalog. Each product node is associated with a specific cache tag. When a product’s price or description is modified, Drupal automatically invalidates the cache entries related to that product’s cache tag. This ensures that users see the updated product information when they visit the corresponding product page.

    Cache Contexts: Cache contexts allow Drupal to vary cache entries based on different conditions, such as user roles, languages, or device types. By leveraging cache contexts, Drupal can serve personalized content while still benefiting from caching. For example, a block containing user-specific recommendations can have cacheability metadata with a cache context for the user’s role. This ensures that each user sees their personalized recommendations while still benefiting from caching for other static elements on the page. Example: Let us suppose our site having multilingual support. Each page can be displayed in different languages, and content translation is managed through Drupal’s translation system. By utilizing cache contexts for language, Drupal can cache different versions of the same page based on the user’s language preference. When a user visits a page, Drupal checks the cache context for the language and serves the cached version of the page specific to that language, if available.

  4. Cache Invalidation: When data changes in Drupal, whether it’s a node being updated, a configuration change, or any other relevant event, Drupal triggers cache invalidation. Cache invalidation involves identifying and invalidating all cache entries associated with the changed data. This ensures that old data is not shown to users.
    Example: Consider an example where inside our site, we have a blog content type, and we have implemented caching for the blog posts with cache tags  [node_of_post_type:id ]. Suppose one of the blog posts having id 5 is updated. Drupal detects this change as it has set the cache tag of post node type as 5 and triggers cache invalidation. It identifies all cache entries associated with the ‘node:5‘ cache tag and marks them as invalid.
  5. Cache Rebuilding: Cache rebuilding occurs when a cache entry is invalidated, and a new cache entry needs to be generated. When a cache miss or a cache entry expiration occurs, Drupal rebuilds the cache by executing the necessary queries and computations to generate fresh cache entries. This process might be resource-intensive, but it ensures that subsequent requests can benefit from the newly generated cache entries.
    Example: Inside the above example, when the next time a user requests the page that displays the list of blog posts, Drupal recognizes that the cache entries for the affected blog post (node 5) are invalidated. It rebuilds the cache by regenerating the HTML output, including the updated content for node 5. The regenerated content is then stored back into the cache storage, replacing the invalid cache entries.

Conclusion: The cache lifecycle in Drupal 9 plays a major role in improving website performance and user experience. By understanding each stage of the cache lifecycle and following best practices, we can effectively leverage caching mechanisms to deliver fast and dynamic web content, which helps to achieve better scalability, improved response times, and enhanced overall performance.

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