Locally managed (LMT) vs. Dictionary managed (DMT) tablespace

The LMT is implemented by adding the extent management local clause to the tablespace definition syntax. Unlike the older dictionary managed tablespaces (DMTs), LMTs automate extent management and keep the Oracle DBA from being able to specify the next storage parameter to govern extent sizes. The only exception to this rule is when NEXT is used with minextents at table creation time.

In a dictionary managed tablespace (DMT), the data dictionary stores the free space details.  While the free blocks list is managed in the segment heard of each table, inside the tablespace), the Free space is recorded in the sys.uet$ table, while used space in the sys.uet$ table.

But with high DML-rate busy tablespaces the data dictionary became a I/O bottleneck and the movement of the space management out of the data dictionary and into the tablespace have two benefits.  First, the tablespace become independent and can be transportable (transportable tablespaces).  Second, locally managed tablespaces remove the O/O contention away from the SYS tablespace.

Segment size management manual vs segment size management auto.

Here is how to migrate the SYSTEM tablespace from dictionary managed to local managed.

< Code   2.20 ? dbms_space_admin_mig_to_local.sql

conn pkg/pkg#123

--How to migrate SYSTEM tablespace from
dictionary managed to locally managed

--Check if you have temporary tablespace other
than SYSTEM

col file_name for a40

select

file_name,

tablespace_name

from

dba_temp_files;

col tablespace_name for a30

select

tablespace_name,

contents

from

dba_tablespaces

where

contents = 'temporary';

--Check if undo tablespace is online (if you are
using automatic undo management)

select

tablespace_name,contents

from

dba_tablespaces

where

contents
= 'undo';

--Put all tablespace in read only mode (do not
include temporary tablespace or tablespaces that has rollback
segments)

select

?alter tablespace '||tablespace_name||' read only;'

from

dba_tablespaces

where

contents <> 'temporary'

and

contents <> 'undo'

and

tablespace_name not in ('SYSTEM','SYSAUX');

'ALTER TABLESPACE'||TABLESPACE_

-----------------------------------------------------------

alter tablespace 
users read only;

alter tablespace 
example read only;

alter tablespace 
apps_ts_tx_data read only;

alter tablespace 
pkg_data read only;

alter tablespace 
pkg_idx read only;

alter tablespace 
pkg_data_32M read only;

alter tablespace 
pkg_idx_32M read only;

alter tablespace 
pkg_data_32M_manual read only;

--Put the database in restricted mode

alter system enable restricted session;

System altered

col host_name for a20

select

instance_name,

host_name,

logins

from

v$instance;

INSTANCE_NAME   
HOST_NAME           
LOGINS

---------------- -------------------- ----------

ora11g          
dbms.f2c.com.br     
restricted

--Change the SYSTEM tablespace

exec
dbms_space_admin.tablespace_migrate_to_local('SYSTEM');

--Verify the tablespace extent management

select

tablespace_name,

extent_management

from

dba_tablespaces

where

tablespace_name = 'SYSTEM';

TABLESPACE_NAME               
EXTENT_MANAGEMENT

------------------------------ -----------------

SYSTEM                        
local

--Disable restricted mode

alter system disable restricted session;

System altered

--Put tablespaces in reead write mode

select

'alter 
tablespace ' || tablespace_name || ' read write;'
from

dba_tablespaces
where

contents <>
'temporary'
and

contents <>
'undo'
and

tablespace_name
not in ('SYSTEM', 'SYSAUX');

'ALTERTABLESPACE'||TABLESPACE_

------------------------------------------------------------

alter 
tablespace users read write;

alter 
tablespace example read write;

alter 
tablespace apps_ts_tx_data read write;

alter 
tablespace pkg_data read write;

alter 
tablespace pkg_idx read write;

alter 
tablespace pkg_data_32M read write;

alter 
tablespace pkg_idx_32M read write;

alter 
tablespace pkg_data_32M_manual read write;

http://www.dba-oracle.com/t_packages_dbms_lmt_vs_dmt.htm