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Question 4: 断片化が減少し、その依存オブジェクトではなく、売上テーブルの未使用領域を再利用したいです。この操作中に、次のことを確認します:
i.長時間実行されるクエリは影響を受けません。
ii.余分なスペースは使用されません。
iii.テーブル上のデータ操作言語（DML）操作はプロセス中にすべての回で成功します。
iv.未使用スペースは最高水位標の上下に再利用されます。
どのALTER TABLEオプションがお勧めですか。
A. DEALLOCATE UNUSED
B. SHRINK SPACE CASCADE
C. SHRINK SPACE COMPACT
D. ROW STORE COMPRESSBASIC
Correct Answer: C
Explanation
The COMPACT clause lets you divide the shrink segment operation into two phases. When
you specify COMPACT, Oracle Database defragments the segment space and compacts the
table rows but postpones the resetting of the high water mark and the deallocation of the
space until a future time. This option is useful if you have long-running queries that might
span the operation and attempt to read from blocks that have been reclaimed. The
defragmentation and compaction results are saved to disk, so the data movement does not
have to be redone during the second phase. You can reissue the SHRINK SPACE clause
without the COMPACT clause during off-peak hours to complete the second phase.
References:
https://docs.oracle.com/cd/B28359_01/server.111/b28310/schema003.htm
