清理 oracle lobsegment

查询到表空间有个对象占用空间非常大，达200G

SQL> select * from (
  2  select owner,segment_name,tablespace_name,segment_type,bytes/1024/1024 from dba_segments order by 5 desc
) where TABLESPACE_NAME='USERS' AND rownum<20;  3  

OWNER                          SEGMENT_NAME
------------------------------ -----------------------------------
TABLESPACE_NAME                SEGMENT_TYPE       BYTES/1024/1024
------------------------------ ------------------ ---------------
UNIGUARD                       SYS_LOB0000052424C00006$$
USERS                          LOBSEGMENT                  204859

UNIGUARD                       IMAGE_FILE
USERS                          TABLE                        10826

UNIGUARD                       CAR_TRACK_10
USERS                          TABLE                         4097

LOBSEGMENT的系统命名规则是

SYS_LOB(10 digit object_id)C(5 digit col#)$$   表段
SYS_IL(10 digit object_id)C(5 digit col#)$$        索引

SQL> select object_name,status from dba_objects where object_id='0000052424';

OBJECT_NAME
--------------------------------------------------------------------------------
STATUS
-------
IMAGE_FILE
VALID

原来是image_file使用了lob字段，为了释放出空间，我把此表导出，重建，再导入。结果空间释放。