Updating Millions Of Rows In A Batch

I have a table which has plenty of rows. In production, I would estimate it to be from 30 millions to 300 millions. I need to update on column (flag) in all the rows (created before certain date).Now saying just:

UPDATE MyTable SET flag = 3 WHERE created < to_date('2010-10-08 23:59:59', 'YY-MM-DD HH24:MI:SS');
COMMIT;

Does not seem like a good idea - the commit-buffer would become too big.I will write a PL/SQL script for this. The question is, whether I should:

a) Update each row separately, and commit after every 10000 rows. ( WHERE RowId = [rowId] )
b) Update 10000 rows with set of dates ( WHERE rowId > [some_row_id] AND RowId < [some_row_id_2]

In the latter example the some_row_ids would naturally be fetched. The rowIds come from sequence. So which one would be more effective?I am not too familiar with PL/SQL or Oracle for that matter.