Is there a mechanism inside of database engines to avoid collisions of non-sequential keys? If so, how does it work?

Say that I create a table that that has a random uuid for a primary key. Is there typically a mechanism inside of the database to gracefully deal with collisions? How does it work? My mind is picturing something simple like "generate a key and check if it exists, and generate another one if it does exist." But if you have a simple non-sequential key, you could end up in this collision loop for quite some time.