1] Insert and Delete are managed in the same fashion as an Update. Redo generation is exactly the same: all the changes to be made to data and undo blocks are first written out to the log buffer.
2] The difference is in the amount of Undo generated. When a row is inserted, the only Undo generated consists of writing out of the new rowid to the undo block. This is because to rollback an Insert the only information Oracle requires is the rowid.
For DELETE: The whole row is written to the undo block, so that the deletion can be rolled back if need by inserting the complete row back into the table.
