如何删除Oracle LOB

Question

以下查询可用于列出用户的数据库对象:

select object_name, object_type from user_objects;

有几个条目,其中object_type是LOB.

如何在Oracle中删除这些LOB对象？

Answer 1

一种情况是,您可以看到LOB user_objects但是连接到user_lobs找不到任何内容,如果该表已被删除,但是在回收站中.

create table t42 (my_clob clob);

table T42 created.

正如预期的那样,贾斯汀的查询显示了专栏:

select l.table_name,
       l.column_name,
       l.segment_name lob_name
  from user_lobs l
       join user_objects o
         on( o.object_name = l.segment_name );

TABLE_NAME  COLUMN_NAME LOB_NAME                     
----------- ----------- ------------------------------
T42         MY_CLOB     SYS_LOB0000133310C00001$$      

drop table t42;

table T42 dropped.

现在贾斯汀的查询没有找到任何东西:

select l.table_name,
       l.column_name,
       l.segment_name lob_name
  from user_lobs l
       join user_objects o
         on( o.object_name = l.segment_name );

no rows selected

但它仍然在user_objects:

select object_name, object_type, status from user_objects
where object_type like 'LOB%';

OBJECT_NAME                    OBJECT_TYPE         STATUS
------------------------------ ------------------- -------
SYS_LOB0000133328C00001$$      LOB                 VALID   

你可以在回收站中看到它:

select * from user_recyclebin;

OBJECT_NAME                    ORIGINAL_NAME                    OPERATION TYPE                      TS_NAME                        CREATETIME          DROPTIME               DROPSCN PARTITION_NAME                   CAN_UNDROP CAN_PURGE    RELATED BASE_OBJECT PURGE_OBJECT      SPACE
------------------------------ -------------------------------- --------- ------------------------- ------------------------------ ------------------- ------------------- ---------- -------------------------------- ---------- --------- ---------- ----------- ------------ ----------
SYS_IL0000133310C00001$$       SYS_IL0000133310C00001$$         DROP      LOB INDEX                 USERS                          2013-08-22:08:33:21 2013-08-22:08:33:21    1.0E+13                                  NO         NO            133310      133310       133310          0 
SYS_LOB0000133310C00001$$      SYS_LOB0000133310C00001$$        DROP      LOB                       USERS                          2013-08-22:08:33:21 2013-08-22:08:33:21    1.0E+13                                  NO         NO            133310      133310       133310          0 
BIN$5IUNXtWkUXLgQwEAAH9TlQ==$0 T42                              DROP      TABLE                     USERS                          2013-08-22:08:33:21 2013-08-22:08:33:21    1.0E+13                                  YES        YES           133310      133310       133310          0 

LOB仍然存在于磁盘上并使用存储,我想这就是你所关心的.因此,为了回答您的问题,要真正删除LOB并释放其存储,您需要清除整个表:

purge table t42;

table purged.

select object_name, object_type, status from user_objects
where object_type like 'LOB%';

no rows selected

有趣的是,如果您命名LOB段,则不会看到此效果:

create table t42 (my_clob clob)
lob (my_clob) store as my_clob_segment;

重复上面的步骤,条目已经从user_objects之后drop.

drop table t42;

table T42 dropped.

select object_name, object_type, status from user_objects
where object_type like 'LOB%';

no rows selected

select * from user_recyclebin;

OBJECT_NAME                    ORIGINAL_NAME                    OPERATION TYPE                      TS_NAME                        CREATETIME          DROPTIME               DROPSCN PARTITION_NAME                   CAN_UNDROP CAN_PURGE    RELATED BASE_OBJECT PURGE_OBJECT      SPACE
------------------------------ -------------------------------- --------- ------------------------- ------------------------------ ------------------- ------------------- ---------- -------------------------------- ---------- --------- ---------- ----------- ------------ ----------
BIN$5IUNXtWnUXLgQwEAAH9TlQ==$0 MY_CLOB_SEGMENT                  DROP      LOB                       USERS                          2013-08-22:08:36:41 2013-08-22:08:36:41    1.0E+13                                  NO         NO            133316      133316       133316          0 
BIN$5IUNXtWoUXLgQwEAAH9TlQ==$0 T42                              DROP      TABLE                     USERS                          2013-08-22:08:36:41 2013-08-22:08:36:41    1.0E+13                                  YES        YES           133316      133316       133316          0 
SYS_IL0000133316C00001$$       SYS_IL0000133316C00001$$         DROP      LOB INDEX                 USERS                          2013-08-22:08:36:41 2013-08-22:08:36:41    1.0E+13                                  NO         NO            133316      133316       133316          0 

当然,存储仍然在使用,你仍然需要清除以释放它,它在数据字典中看起来更加一致.所以这看起来像一个(非常小的)bug,也许最多.它可能与支持说明394442.1中提到的行为有关.