635.While Monitoring the space usage in your database that is in ARCHIVELOG mode you observed that
the flash recovery area does not have enough free space to accommodate any more files and you do not
have necessary permissions to add more space to it.
Identify the two events that can occur in the event of a log switch? (Choose two.)
A. An entry is created in the alert log file and the database instance continues to function normally
B. The log switch hangs occur for transactions until free space is available in the flash recovery area
C. The Oracle database server deletes a file that is on the obsolete file list to make free space in the flash
recovery area
D. The database instance status is implicitly changed to RESTRICTED mode and file creations to the
flash recovery area are prevented
Answer: BC
解析：在歸檔模式下，你的閃回恢復區空間不足，你又沒有許可權增加空間，問當你切換日誌時，會發生什麼？

首先你應該瞭解閃回恢復區的都有哪些內容：所有和恢復相關的檔案都可以存放到閃回恢復區

SQL>select file_type from v$flash_recovery_area_usage;
FILE_TYPE
------------------------
CONTROLFILE
ONLINELOG
ARCHIVELOG
BACKUPPIECE
IMAGECOPY
FLASHBACKLOG
已選擇6行。

上面的檢視中可以看出，包括controfile,online redo logfile,archive logfile,rman backuppiece,rman image copy, flashback log等，都可以利用閃回恢復區來存放、管理。

B選項：閃回恢復區空間不足導致不能歸檔，而日誌切換時，會觸發歸檔，所以就會導致事務掛起，因為事務發生之前，要先寫日誌，不能歸檔，也就不能寫日誌，所以事務要掛起，B選項對，

C選項:伺服器程式會根據備份保留策略來刪除過期的本分檔案，來釋放一些空間，故C正確。

Oracle 資料庫OCP-053-635

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