OCP-1Z0-053-V12.02-277题

277.The BOOKINGS table contains online booking information. When a booking is confirmed, the details

are transferred to an archival table BOOKINGS_HIST and deleted from the BOOKINGS table. There is no

fixed time interval between each online booking and its confirmation. Because sufficient space is not

always available from the delete operations the high-water mark (HWM) is moved up and many rows are

inserted below the HWM of the table. The BOOKINGS table has Automatic Segment Space Management

(ASSM) and row movement enabled. The table is accessible in 24x7 mode.

What is the most efficient method to reclaim the space released by the delete operations in the

BOOKINGS table?

A. Perform EXPORT, DROP, and IMPORT operations on the BOOKINGS table sequentially

B. Shrink the BOOKINGS table by using the ALTER TABLE... SHRINK SPACE command

C. Move the BOOKINGS table to a different location by using the ALTER TABLE... MOVE command

D. Deallocate the space in the BOOKINGS table by using the ALTER TABLE ... DEALLOCATE UNUSED

command

Answer: B

答案解析：

参考：http://blog.csdn.net/rlhua/article/details/13431595

使用SQL 收缩段

因为在按堆组织的段中，收缩操作可能会导致ROWID发生更改，所以在该段上执行收缩操作之前，必须在相应段上启用行移动。默认情况下，在段级别上行移动处于禁用状态。

要启用行移动，需要使用CREATE TABLE或ALTER TABLE命令的ENABLE ROW MOVEMENT子句。

使用ALTER命令可以针对对象调用段收缩。对象可以是下列类型之一：表（按堆组织的表或索引表）、分区、子分区、LOB（数据和索引段）、索引、实体化视图或实体化视图日志。

使用SHRINK SPACE子句可以收缩段中的空间。如果指定了CASCADE，则收缩行为将级联到所有支持收缩操作的从属段，但实体化视图、LOB 索引和IOT（索引表）映射表例外。