You are working on a database that must be functioning 24 hours a day, 7 days a week. The database is configured in ARCHIVELOG mode.
Which two options do you have for performing user-managed backups? (Choose two.)
A.You can perform consistent backups only.
B.You can perform a complete database backup without shutting down the database instance.
C.You can back up data files only when all data files have the same SCN recorded in the control file.
D.You can back up only those data files whose headers are frozen by using ALTER TABLESPACE BEGIN BACKUP or ALTER DATABASE BEGIN BACKUP commands.
归档模式：可以进行一致性备份（冷备）和非一致性备份（热备）。
非归档模式：一致性备份（冷备）
一致性备份（冷备份）：在数据库正常关闭情况下做备份，数据库处于一致性状态。
（可以用于归档和非归档），所有 SCN 号一致。缺点：数据库需要关闭。
非一致性备份（热备份）：数据库在 open 状态下备份（用于归档模式），
使用 alter database/tablespace xxx begin backup 开始备份,此时会冻结数据文件文件头。