Turning autocommit off ( a silly design "feature" of the jdbc standard -- having autocommit on, sorts of removes the "transaction" from the database) will ensure that all work you perform up until you commit is able to be rolled back if you rollback.

Redolog sizing is important for performance but will not hinder you in this respect.

Rollback segment sizing is perhaps more important. You need to ensure they are large enough to hold your rollback information.