When would you want to use disable_ddl_transaction in Rails?

Question

My understanding is that all migrations are wrapped in a transaction, meaning, if a change for 1 row, like adding null: false, in a table fails, every other row will fail. When would you not want this to happen with disable_ddl_transaction?

Answer 1

All migrations are wrapped in transaction by default so that they can be rolled back when they are failed.

You need to use disable_ddl_transaction when you want to do something that can not excute inside a transaction. You can check Transactional Migrations section of Migration document for example.