It would be nice if you added a how it works section to the readme. Knowing that it does `begin; ${query}; rollback;` under the hood is important. The example with truncate in fact made me think the opposite was true, since truncate violates MVCC and cannot be rolled back.

I’m often worrying about locks in migrations that could be long running, so executing the query to figure out the locks defeats the purpose. Or at least I need to know to use a test DB.