单项选择题
A.The extents in undo tablespace retain data until the next full database backup.
B.The extents containing committed data in the undo tablespace are never overwritten.
C.The extents which no longer contain uncommitted data in the undo tablespace are not overwritten for at least15 minutes.
D.The extents containing committed data in the undo tablespace are not overwritten until the instance is shut down.
多项选择题 A user receives the following error while executing a query： ORA01555：snapshot too old Which two options can be the solutions to avoid such errors in future？（）
多项选择题 User SCOTT executes the following command on the EMP table but has not issued COMMIT， ROLLBACK，or any data definition language （DDL） command： SQL> SELECT job FROM emp 2 WHERE job=’CLERK’ FOR UPDATE OF empno SCOTT has opened another session to work with the database. Which three operations would wait when issued in SCOTT’s second session？（）
多项选择题 WhichtwoarevalidlockinglevelsthatareusedbytransactionsinanOracledatabase？（）