Of course re-booting servers or re-starting processes forces app servers to re-cache data, database servers re-parse, re-cache and re-optimize queries and throw

Of course re-booting servers or re-starting processes forces app servers to re-cache data, database servers re-parse, re-cache and re-optimize queries and throws away good query plans & replaces them with new versions, some of which will be worse than what you had. On apps that cache database objects in app server memory, we see a noticeable degrade of response time while the app server re-caches database objects.