Oracle OCP 1Z0 053 Q96(Shrink Space Compact)

96.Examine the following command:
SQL> ALTER TABLE booking SHRINK SPACE COMPACT;
Which activity is performed when the preceding command is executed?
A. The shrink operation touches every block in the BOOKING table
B. The high-water mark (HWM) for the BOOKING table is shifted from its original position
C. The progress of the shrink operation is saved in the bitmap blocks of the BOOKING table
D. The data manipulation language (DML) triggers on the BOOKING table are executed because the
shrink operation is internally handled by the INSERT/DELETE operation
Answer: C


compact不會做釋放高水位的動作

如果有長時間執行的查詢，而且這些查詢可能跨越收縮操作，並嘗試從已回收的塊中讀取資料，則COMPACT子句會很有用。指定SHRINK SPACE COMPACT子句時，收縮操作的進度將儲存在相應段的點陣圖塊中。這意味著下次在同一個段上執行收縮操作時，Oracle DB Server 可以記住已經執行過的操作。然後你就可以在非峰值時段重新發出SHRINK SPACE子句，無需使用COMPACT子句即可完成第二階段

參考：http://blog.csdn.net/jgmydsai/article/details/37350269
         http://blog.csdn.net/rlhua/article/details/13431595

來自 “ ITPUB部落格 ” ，連結：http://blog.itpub.net/8520577/viewspace-2073842/，如需轉載，請註明出處，否則將追究法律責任。