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impdp remap_tablespace parameter

Expert Oracle Database Tips by Donald BurlesonMarch 25, 2015

RMAN Using remap_tablespace to Import Objects to a Different Tablespace

Being a DBA, there are plenty of times when you have to move the objects around the tablespaces to get them reorganized. This can be done in many ways; for example, using the alter table move command or the dbms_redefinition package. One of the easy ways to do so is to the use the remap_tablespace switch. As the name suggests, this option moves the object from the source tablespace to the target tablespace. To see this in action, make a table and explicitly create some fragmentation in it.

test@orcl112> create table t as select * from dba_objects;
table created. 

test@orcl112> exec dbms_stats.gather_table_stats(user, 't');
PL/SQL procedure successfully completed. 

test@orcl112> select sum(bytes) , sum(blocks) from dba_extents where segment_name='t';

SUM(BYTES) SUM(BLOCKS)
---------- -----------
   9568256        1168
1 row selected.

test@orcl112> delete t;
72615 rows deleted. 

test@orcl112> commit;
commit complete.
test@orcl112> exec dbms_stats.gather_table_stats(user, 't');
PL/SQL procedure successfully completed. 

test@orcl112> select sum(bytes) , sum(blocks) from dba_extents where segment_name='t';

SUM(BYTES) SUM(BLOCKS)
---------- -----------
   9568256        1168
1 row selected.

So you can see that even after the complete delete, the table does not release the used space and it is reported again.

Check which tablespace the object belongs at the moment.

test@orcl112> select table_name, tablespace_name from dba_tables where table_name='t' and owner='test';

TABLE_NAME                     TABLESPACE_NAME
------------------------------ ------------------------------
T                              USERS

1 row selected.

This shows that it is the users tablespace at the moment. Though not good but for the sake of this demonstration, move the table to the system tablespace using Data Pump. Export the table first:

E:\>expdp test/test directory=dp dumpfile=exptab.dmp tables=T

Now use the import command and the remap_tablespaceswitch to move the object into a different tablespace. Also, since the table is already there in the schema, you have to use the switch table_exists_action with its value replace. Check it out in action:

E:\>impdp test/test directory=dp dumpfile=exptab.dmp table_exists_action=replace  remap_tablespace=users:system

Check the tablespace of the object to see whether it has changed or not:

SQL>
select
 tablespace_name, table_name
from
 dba_tables
where
 table_name='t' and owner='test';

TABLESPACE_NAME                TABLE_NAME
------------------------------ ------------------------------
SYSTEM                         T

Using table_exists_action Parameter

When importing a table, Data Pump skips the job if the object already exists in the imported schema. However, by using the table_exists_action parameter with its available values, it is possible to bypass skipping the table import. This parameter accepts the following values:

  • skip:  Is the default value and used to skip importing the table if it already exists

  • append:  Appends the data to an already existing table

  • truncate:  Truncates the already existing table and imports fresh data

  • replace:  Drops already an existing table and creates a new one with fresh data

The next example demonstrates the usage of the above values. For this, create a table with one row:

SQL>
create
 table tbl_test (id number);
Table created. 

SQL>
insert into
 tbl_test values(1);
1 row created. 

SQL>
commit;
Commit complete.
SQL>

Now export the table:

expdp usr1/usr1 directory=dp_dir dumpfile=test.dmp tables=tbl_test

Using the skip value:

skip is the default value and it will just abort the process by saying that the table already exists.

impdp usr1/usr1 directory=dp_dir dumpfile=test.dmp table_exists_action=skip

ora-39151: table "usr1"."tbl_test" exists. All dependent metadata and data will be skipped due to table_exists_action of skip

Using the append value:

C:\>impdp usr1/usr1 directory=dp_dir dumpfile=test.dmp table_exists_action=append

ORA-39152: Table "usr1"."tbl_test" exists. Data will be appended to existing table but all dependent metadata will be skipped due to table_exists_action of append

Now check the table. Since import used the append value for the table_exists_action parameter, there should be two rows:

SQL>
select * from
 tbl_test; 

        ID
----------
         1
         1

Using truncate and replace values:

Both values give the same result; however, the first just truncates the table, where the second value drops and recreates it.  It is shown here in one example:

C:\>impdp usr1/usr1 directory=dp_dir dumpfile=test.dmp table_exists_action=truncate

ora-39153: table "usr1"."tbl_test" exists and has been truncated. Data will be loaded but all dependent metadata will be skipped due to table_exists_action of truncate

C:\>impdp usr1/usr1 directory=dp_dir dumpfile=test.dmp table_exists_action=replace

The replace value will not give an informative message and just drops and recreates the table with new values.

 

 

 
 
 
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