Analyze Method Cache Invalidation in Ruby and how it affects production application performance.

Ruby uses global and localized method caches to speed up lookups. Modifying any class definition or defining methods dynamically invalidates these caches, causing global lookup performance hits.

To prevent walking the full ancestor tree on every method call, Ruby caches method lookups in a global table and via inline caches at the call site. When a class is reopened, a module is included, or a dynamic method is defined via define_method or extend, Ruby increments a global class serial number. This instantly invalidates the method caches across the entire application runtime, forcing Ruby to re-resolve methods through full ancestor lookups. If done continuously during runtime requests, performance degrades significantly.