Automated Tool Identifies Cache Tag Issue Behind 4.2-Second Drupal Page Loads

Souvik explained that the development team had spent approximately three weeks investigating the slowdown. They reviewed database performance, optimised queries, integrated Redis, and adjusted PHP-FPM settings. None of those measures produced significant improvement.

The issue was analysed using a tool called EventHorizon, which flagged a custom module responsible for rendering product recommendations. The render array lacked cache tags for the product entities it displayed.

Without proper cache metadata, Drupal’s caching system could not determine content dependencies. As a result, the recommendation block was rebuilt on every request, triggering repeated entity loading, execution of recommendation logic, and reconstruction of the render array.

The fix required adding the appropriate cache tags. According to Souvik, the adjustment involved a single line of code and resulted in a significant reduction in page load time.

Souvik noted that cache tag issues can be difficult to detect through manual code review because the code appears functionally correct while failing to declare cache dependencies. He argued that automated analysis tools are well suited to identifying consistent structural patterns such as missing cache metadata, allowing developers to focus on architectural decisions.