This is a question that came in through email from a prior student, which I’ll summarize as: with a distributed availability group, what are the semantics of log truncation?
As I’m not an AG expert (I just know enough to be dangerous ha-ha), I asked Jonathan to jump in, as he is most definitely an AG expert! I’ll use AG for availability group and DAG for distributed availability group in the explanation below. Whether the AGs in question have synchronous or asynchronous replicas is irrelevant for this discussion.
Read on for the answer.