ENABLE ROW MOVEMENT

Since the ALTER TABLE SHRINK command appeared and "ENABLE ROW MOVEMENT" has been presented as a requirement, some DBAs have been confused about what it means to enable row movement.

This does *NOT* cause Oracle to automatically move a row. However, a row may be moved as a result of action by the DBA (e.g. ALTER TABLE SHRINK) or a User / Application. The latter is the case where a row in a Partitioned Table has to move from one Partition to another because the Partition Key itself in that row has been updated.
Note that updating the Partition Key (such that a row actually moves to another Partition) is frowned upon and is not enabled by default. In the rare case where your design has a flaw that rows have to move between Partitions, you need to ENABLE ROW MOVEMENT.

In the example below, a row has to move from the 'SG' Partition to the 'IN' Partition. This is disallowed by Oracle until and unless the DBA ENABLEs ROW MOVEMENT :

SQL> -- create a "normal" partitoned table
SQL> drop table my_emp_tbl purge;

Table dropped.

SQL> create table my_emp_tbl
  2  (emp_id   number not null primary key,
  3   country_id  varchar2(2),
  4   emp_name varchar2(50),
  5   join_date date)
  6  partition by list (country_id)
  7  (
  8  partition my_emp_tbl_in values ('IN'),
  9  partition my_emp_tbl_sg values ('SG'),
 10  partition my_emp_tbl_us values ('US')
 11  )
 12  /

Table created.

SQL> 
SQL> insert into my_emp_tbl
  2  select rownum,
  3  decode(mod(rownum,3),0,'IN',1,'SG',2,'US'),
  4  dbms_random.string('X',40),
  5  sysdate-365+rownum
  6  from dual connect by level < 100
  7  /

99 rows created.

SQL> 
SQL> commit;

Commit complete.

SQL> 
SQL> -- collect statistics on row counts
SQL> exec dbms_stats.gather_table_stats('','MY_EMP_TBL',estimate_percent=>100,granularity=>'ALL');

PL/SQL procedure successfully completed.

SQL> select partition_name, num_rows
  2  from user_tab_partitions
  3  where table_name = 'MY_EMP_TBL'
  4  order by partition_position
  5  /

PARTITION_NAME                   NUM_ROWS
------------------------------ ----------
MY_EMP_TBL_IN                          33
MY_EMP_TBL_SG                          33
MY_EMP_TBL_US                          33

SQL> 
SQL> -- identify employee 4
SQL> select * from my_emp_tbl where emp_id = 4;

    EMP_ID CO EMP_NAME
---------- -- --------------------------------------------------
JOIN_DATE
---------
         4 SG 9WSXMYH66V6I8B1LKKW7YRTG2VYQGY2OPIT54OFW
16-JUL-10


SQL> -- change the employees country
SQL> update my_emp_tbl set country_id = 'IN' where emp_id = 4;
update my_emp_tbl set country_id = 'IN' where emp_id = 4
       *
ERROR at line 1:
ORA-14402: updating partition key column would cause a partition change


SQL> 
SQL> -- enable row movement
SQL> alter table my_emp_tbl enable row movement;

Table altered.

SQL> update my_emp_tbl set country_id = 'IN' where emp_id = 4;

1 row updated.

SQL>  

So it is not just ALTER TABLE SHRINK that the ENABLE ROW MOVEMENT is necessary for. Yet, it is likely a defect in your design if you have frequent movements of rows between Partitions. Remember that GLOBAL and LOCAL Indexes have to be updated.
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