Commit vs Rollback

A quick, but I hope interesting note: the commit operation in Oracle database is very fast (actually oracle is doing a fast commit), as opossed to rollback, which may take as long as the operation that is being rolled back. Thinking of it, before comitting, most of the work is done already, except for writing the dirty buffers to disk and the information to redo logs, while the rollback has to read data back from the disk (UNDO tablespace) and apply it to the data files. So oracle is having an optimistic approach and I guess they are right, most of the time the changes are comitted, rather than rolled back.