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.

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;

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