Kenneth Fisher explains deadlock priority:
Everyone deals with deadlocks from time to time. But sometimes we need to control who’s the deadlock victim and who isn’t. For example, I’m doing a big delete on a table in a 24×7 environment, I can’t afford downtime to do it so I’m doing my delete in small chunks to reduce transaction size and blocking time. My delete needs to happen but I’m in no hurry and I really can’t afford to deadlock some other transaction. So how do I make sure?
Or on the other hand, I’m running an update that absolutely has to happen right now. It’s going to take a bit and I can’t afford the time for it to be started over. A deadlock would be a disaster. What do I do?
That’s where deadlock priority comes into play.
Click through for the explanation.