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
Explanation:
http://www.oracle-base.com/articles/10g/SpaceObjectTransactionManagement10g.php
Based on the recommendations from the segment advisor you can recover space from specific
objects using one of the variations of the ALTER TABLE … SHRINK SPACE commands. The
shrink is accomplished by moving rows between blocks, hence the requirement for row movement
to be enabled for the shrink to take place. This can cause problem with ROWID based triggers.
The shrinking process is only available for objects in tablespaces with automatic segment-space
management enabled. The COMPACT option allows the shrink operation to be broken into two
stages. First the rows are moved using the COMPACT option but the HWM is not adjusted so no
parsed SQL statements are invalidated. The HWM can be adjusted at a later date by reissuing the
statement without the COMPACT option. At this point any depenedant SQL statements will need
to be reparsed.
http://books.google.com/books?id=0iwrL9P25Z0C&pg=PA190&lpg=PA190&dq=shrink+operation+
is+saved+in +the+bitmap
+blocks&source=bl&ots=MGoTq9AT0m&sig=y0EgXfO2MZnWlOZTgKXo5CDbFJw&hl=en&ei=L0g
ATdqaNsG1
nAfsrZjlDQ&sa=X&oi=book_result&ct=result&resnum=4&ved=0CCcQ6AEwAw#v=onepage&q=shrink% 20operation%20is%20saved%20in%20the%20bitmap%20blocks&f=false A shrink operation
may cause ROWIDs to change in heap-organized segments. So row movement has to be enabled
to circumvent this issue before a shrink operation. To enable row movement, use the {CREATE|
ALTER} TABLE ENABLE ROW movement command. A shrink operation consists of thw
phases, compaction and adjusting the HWM to release the unused space. If the COMPACT option
is used, only the first phase is executed. The shrink results are saved in bitmap blocks of the
corresponding segment, Oracle 10g will remember what has been done. If CASCADE is specified,
the shrinking cascades to all dependent segments that support a shrink operation. During the
COMPACT phase, individual rowlocks are held. Concurrent DML operations serialize on thes
rowlocks and DML operations can block the compaction progress. When the HWM is adjusted in
the second phase, the object is locked in exclusive mode for a short duration.