Service at work creeps up to its limit every three days. Nobody knows why, and everyone's sure it's somebody else's. So: jcmd <pid> GC.heap_dump, 11GB file, drag it into Eclipse MAT and wait.
Dominator tree. A static HashMap "cache" with no eviction, in a helper class from 2016 whose author left in 2018. Key includes the request timestamp, so nothing has ever hit. It's the world's most expensive append-only log.
Don't need help, just needed to tell someone.