About
In a locally managed tablespace, there are two methods that Oracle Database can use to manage segment space:
- automatic
- and manual.
To manage free space in the segment:
- Manual segment space management uses linked lists called “freelists”
- Automatic segment space management uses bitmaps.
Automatic segment space management is the more efficient method, and is the default for all new permanent, locally managed tablespaces.
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Maintenance
Default
Automatic segment space management is the default for all new permanent, locally managed tablespaces.
Create
- Automatic (ASSM)
CREATE TABLESPACE lmtbsb DATAFILE '/u02/oracle/data/lmtbsb01.dbf' SIZE 50M
EXTENT MANAGEMENT LOCAL
SEGMENT SPACE MANAGEMENT AUTO; -- ASSM is enabled
- Manual
CREATE TABLESPACE lmtbsb DATAFILE '/u02/oracle/data/lmtbsb01.dbf' SIZE 50M
EXTENT MANAGEMENT LOCAL
SEGMENT SPACE MANAGEMENT MANUAL; -- ASSM is disbaled
Modify
You cannot change the segment space management mode of a tablespace.
View
select tablespace_name, segment_space_management from dba_tablespaces;
TABLESPACE_NAME | SEGMENT_SPACE_MANAGEMENT |
---|---|
SYSTEM | MANUAL |
SYSAUX | AUTO |
UNDOTBS | MANUAL |
TEMP | MANUAL |
USERS | AUTO |