Oracle 11g新特性延迟段创建和truncate的增强

SQL> select * from tab;

TNAME                          TABTYPE  CLUSTERID
------------------------------ ------- ----------
TEST1                          TABLE

SQL> select segment_name,bytes from user_segments;        ----还没有给分配空间

no rows selected

SQL> insert into test1 select * from dba_objects where rownum<2;     -----插入一行记录

1 row created.

SQL> select segment_name,bytes from user_segments;       ----分配空间

SEGMENT_NAME                        BYTES
------------------------------ ----------
TEST1                               65536

SQL> commit;

Commit complete.

SQL> alter table test1 allocate extent;          ------手动给表分配一个区

Table altered.

SQL> select segment_name,bytes from user_segments;

SEGMENT_NAME                        BYTES
------------------------------ ----------
TEST1                              131072

SQL> truncate table test1;          ------使用不加子句的truncate

Table truncated.

SQL> select segment_name,bytes from user_segments;       -----只是删除到最小的区

SEGMENT_NAME                        BYTES
------------------------------ ----------
TEST1                               65536
 
SQL> truncate table test1 drop all storage;         -----使用11g中新加的子句drop all stroage

Table truncated.

SQL> select segment_name,bytes from user_segments;      -----段全部被回收

no rows selected