Diagnosing a slow Rails page, layer by layer

A slow Rails page can be diagnosed by breaking down the request into its individual layers, including middleware, controller, SQL, view, external calls, and browser. The most common causes of slowness are identified in each layer, and tools like rack-mini-profiler and bullet can be used to pinpoint the issue. In this example, an N+1 query problem was found in the view layer, which was fixed by preloading the attachment using Active Storage's with_attached_image method. This can help to significantly reduce the number of queries and improve page load times.