Undo tablespace/redo logs/ DML /DDL/ truncate/ delete

Question

1st scenario:Delete
10 rows in a table
Delete 5 rows
5 rows in the table
savepoint sp1
Delete 3 rows
2 rows in the table
rollback to savepoint sp1
5 rows in the table
So all DML affected values are noted in the undotablespace and present in the undotablespace until a commit is issued.And also redo logs make note of DML statements.AM I RIGHT??????
2nd scenario-truncate
10 rows in table
savepoint sp1
truncate
0 rows in table
rollback to savepoint sp1 gives this error
ORA-01086: savepoint 'SP2' never established
So is truncate [are all DDL statements] noted in the undo tablespace and are they noted in the redologs????????
I KNOW THAT A DML IS NOT AUTOCOMMIT AND A DDL IS AN AUTOCOMMIT

Answer 1

When you issue a delete is the data really deleted ?WHen you issue a delete, there is a before image of the data recorded to the undo area. (And that undo information itself is forwarded to the redo.) Then the data is actually deleted from the 'current' block as represented in memory.
Therefore, the data is actually deleted, but can be recovered by rolling back until a commit occurs.
It can also be recovered using flashback techniques which simply rebuild from the undo.
When you issue a truncate is the data really deleted
or is the high water mark pointer for a datablock lost?The data is not deleted. Therefore there is no undo record of the data 'removal' to be rolled back.
The high water mark pointer is reset. It's old value is in the undo, but the truncate is a DDL command, and it is preceded and followed by an implicit commit, voiding any potential rollback request.
I mean you can always rollback a delete and not
rollback a truncate?Correct - using standard techniques, deletes can be rolled back and truncates can not.