339.Why would you run the delete obsolete command? (Choose all that apply.)
A. To remove missing backup set pieces physically from disk
B. To remove metadata related to backup set pieces in the control file and the recovery catalog
C. To mark as deleted records in the control file and the recovery catalog associated with obsolete backup sets
D. To delete backup set pieces associated with backups that are no longer needed due to retention criteria
E. To remove old versions of RMAN backups
Answer: CD
答案解析：
delete obsolete删除任何过时的备份。
包括控制文件里和恢复目录里的过时的备份集，而过时指的是超过了指定的备份策略的不再需要恢复的备份集。