迁移数据时LOB对象统计差异问题

使用Datapump做数据迁移前，都会统计各种类型的对象数目，便于迁移后进行比对。但在一次数据迁移后，发现LOB对象数目对不上。源库版本是12.2.0.1，目标版本是11.2.0.4。开始猜测是版本差异，统计LOB对象有些差异，仔细调查后发现，不是这么回事。

# 普通表不含 LOB 列
SQL> create table t1 (id int, name varchar2(10));

Table created.

SQL> insert into t1 values(1, 'huayd');

1 row created.

SQL> commit;

Commit complete.

# 回收站无对象
SQL> show recyclebin;

SQL> drop table t1;

Table dropped.

SQL> show recyclebin;
ORIGINAL NAME    RECYCLEBIN NAME                OBJECT TYPE  DROP TIME
---------------- ------------------------------ ------------ -------------------
T1               BIN$d4rf0DuSPdrgUxZvAgpzaw==$0 TABLE        2018-10-06:15:01:32

# table删除后，dba_objects不再该table的纪录    
SQL> select OWNER, OBJECT_NAME from dba_objects where OWNER='HUAYD';

no rows selected

# 创建含 LOB 列的对象
SQL> create table t1 (id int, name varchar2(10), col_lob clob);

Table created.

SQL> purge recyclebin;

Recyclebin purged.

SQL> 
SQL> insert into t1 values(1, 'huayd', 'test');

1 row created.

SQL> commit;

Commit complete.

SQL> select OWNER, OBJECT_NAME from dba_objects where OWNER='HUAYD';

OWNER           OBJECT_NAME
--------------- ------------------------------
HUAYD           SYS_IL0000092503C00003$$
HUAYD           T1
HUAYD           SYS_LOB0000092503C00003$$

SQL> select OWNER, OBJECT_NAME,object_type from dba_objects where OWNER='HUAYD';

OWNER           OBJECT_NAME                    OBJECT_TYPE
--------------- ------------------------------ -------------------
HUAYD           SYS_IL0000092503C00003$$       INDEX
HUAYD           T1                             TABLE
HUAYD           SYS_LOB0000092503C00003$$      LOB

SQL> 
SQL> drop table t1;

Table dropped.

SQL> show recyclebin;
ORIGINAL NAME    RECYCLEBIN NAME                OBJECT TYPE  DROP TIME
---------------- ------------------------------ ------------ -------------------
T1               BIN$d4rf0DuTPdrgUxZvAgpzaw==$0 TABLE        2018-10-06:15:06:40

 # 含 LOB 列的对象，被drop后，dba_objects里仍保留LOB对象的纪录，这也就是数据导出再导入后，对象数目不一致的地方
SQL> select OWNER, OBJECT_NAME,object_type from dba_objects where OWNER='HUAYD';

OWNER           OBJECT_NAME                    OBJECT_TYPE
--------------- ------------------------------ -------------------
HUAYD           SYS_LOB0000092503C00003$$      LOB

SQL> 

结论：含LOB的对象被drop后，在dba_objects中仍有纪录，但是使用Datapump进行数据导出时，并不会导出回收站内的对象，因此最后数据导入后，对比对象数目时会有差异。

--End
Mason