It's a new term to me, but I think “selective LIFO” means switching to LIFO scheduling under overload conditions as a load-shedding measure: https://landing.google.com/sre/sre-book/chapters/addressing-...

Presumably “queue depth determination”, another new term for me, means determining how big the queue of pending requests for a service is allowed to get before further requests are refused (another load shedding measure) rather than being enqueued.