The STORAGE clauses let you determine what happens to the space freed by the
truncated rows. The DROP STORAGE clause and REUSE STORAGE clause also apply to
the space freed by the data deleted from associated indexes.

DROP STORAGE
Specify DROP STORAGE to deallocate all space from the deleted
rows from the table or cluster except the space allocated by the MINEXTENTS
parameter of the table or cluster. This space can subsequently be used by other objects
in the tablespace. Oracle Database also sets the NEXT storage parameter to the size of
the last extent removed from the segment in the truncation process. This is the default.
保留MINEXTENT空间，其余空间可供后续的对象使用
设置NEXT存储参数为truncate进程最后移除的范围大小

REUSE STORAGE
Specify REUSE STORAGE to retain the space from the deleted rows
allocated to the table or cluster. Storage values are not reset to the values when the
table or cluster was created. This space can subsequently be used only by new data in
the table or cluster resulting from insert or update operations. This clause leaves
storage parameters at their current settings.
If you have specified more than one free list for the object you are truncating, then the
REUSE STORAGE clause also removes any mapping of free lists to instances and resets
the high-water mark to the beginning of the first extent.
保留已分配的空间
移除free list
重置HWM