The Anatomy of Hanging: When the Thread Pool Is Over and the CPU Is Almost Empty

Let's look at why the Spring MVC service can freeze when the CPU is low: the queue accumulates not in the processor, but in Tomcat/Hikari/HTTP pools and waits for external dependencies. You'll get a minimal set of metrics (RED+USE), a short diagnostic playlist, and practical fixes: timeouts, bulkhead/limits, pool matching, and saturation alerts.