Any DDL worthy of the name (table rewrite needed) in MySQL needs to be done with pt-online-schema-change or gh-ost. With DDL, you want to e.g. have it tune the I/O load of the migration so it doesn't interfere too much with production load. In practice, pt-osc / gh-ost means you have a kind of transaction, because the rewritten table doesn't take the place of the old one until the rename at the end. That's essentially an atomic commit.