Which two statements are true regarding transactions in an Oracle database? (Choose two.)
A.
Multiple transactions can use the same undo segment.
B.
A transaction is assigned an undo segment when it is started.
C.
More than one transaction cannot share the same extent in the undo tablespace.
D.
The transactions use system undo segment to store undo data if all the segments in the undo
tablespace are used.
Undo segments will be assigned when the transaction begins. Throughout the course of the transaction, the time change data (before the change) the original value is copied to the undo segment. By checking the V $ TRANSACTION dynamic performance view, you can see which transactions are assigned to which undo segments.
Undo segments to support transaction processing, a dedicated section created automatically by the instance. Like all segments, like the reduction section composed by the district, the district and the data blocks. Undo segments as needed automatically grow and shrink, it acts as a buffer storage loop assigned transaction.
Transaction fills its reduction stage area until the completion of the transaction or taking up all the space so far.
If after you’ve filled out area also need more space, the transaction is to obtain space segment to the next area. After all occupied areas, the transaction will be automatically transferred back to the first area or segment allocation request to restore the District.
Note: Parallel DML and DDL operations can actually lead to reduction of transaction processing using a plurality of segments.
A Answer: multiple transactions can share the same undo segment
B Answer: When the transaction will initially allocate undo segments.
C Answer: multiple transactions can share the same undo segments, including the area that also can share the same area.
D Answer: After undo table space all segments are filled, the transaction will be automatically transferred back to the first area or segment allocation request to restore the District.
If you can not assign new area, it is possible to overwrite the original undo data, or error.