es (single ST enqueue) 减少对数据字典表的争用。
Locally managed tablespaces eliminate the need to periodically coalesce free space (automatically tracks adjacent free space) 不需要定期合并空闲空间。
Changes to the extent bitmaps do not generate rollback information 对于位图区的改变不会产生回滚信息。
Locally ManagedSYSTEM Tablespace:
From Oracle9irelease 9.2 one can change the SYSTEM tablespace to locally managed. Further, ifyou create a database with DBCA (Database Configuration Assistant), it willhave a locally managed SYSTEM tablespace by default. The following restrictionsapply:
No dictionary-managed tablespace in the database can be READ WRITE.
You cannot create new dictionary managed tablespaces
You cannot convert any dictionary managed tablespaces to local
Thus, it is bestonly to convert the SYSTEM tablespace to LMT after
all other tablespaces are migrated to LMT.
自920后数据字典管理表空间已被废弃！
Segment SpaceManagement in LMT: 本地管理表空间中的段管理
From Oracle 9i,one can not only have bitmap managed tablespaces, but also bitmap managedsegments when setting Segment Space Management to AUTO for a tablespace. Lookat this example:设置段自动管理
SQL> CREATE TABLESPACE ts4 DATAFILE '/oradata/ts4_01.dbf'SIZE 50M
EXTENT MANAGEMENT LOCAL
SEGMENT SPACE MANAGEMENT AUTO;
Segment SpaceManagement eliminates the need to specify and tune the PCTUSED, FREELISTS, andFREELISTS GROUPS storage parameters for schema objects. The Automatic SegmentSpace Management feature improves the performance of concurrent DML operationssignificantly since different parts of the bitmap can be used simultaneouslyeliminating serialization for free space lookups against the FREELSITS. This isof particular importance when using RAC, or if "buffer busy waits"are deteted.
Convert betweenLMT and DMT: 本地管理与数据字典管理表空间转换
TheDBMS_SPACE_ADMIN package allows DBAs to quickly and easily
convert between LMT and DMT mode. Look at these examples:
SQL> exec dbms_space_admin.Tablespace_Migrate_TO_Local('ts1');
PL/SQL procedure successfully completed.?
SQL> execdbms_space_admin.Tablespace_Migrate_FROM_Local('ts2');
PL/SQL procedure successfully completed.?
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