What is the absolute fastest way to swap a directory and all its contents?

Rino Bino asked:

I have a regular task that I need to swap out a live/accessed dir with a new version of it.

• There is a live dir with resources in it: dir/
• Goal is to swap this out with dir_new/ and cause as little disruption in access to the dir.
• The content is live/accessed. Stopping access to the directory from end users is out of scope. I would just do this during a downtime window otherwise.

Here’s how I do it now:

mv dir dir_old && mv dir_new dir

This works fine, but I’m not sure if any experts have a faster/more reliable way?

• The filesystem is xfs
• The "new" dir cannot have ANY content from the existing dir in it, so moving in place, dealing with files didn’t seem like it would work.
• Perhaps rsync with a --delete option? However a requirement is to change "everything" at once in the dir. In other words I can’t have a mix of files from the new and old mixed together.