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Oracle Tips by Burleson

Oracle9i Tablespace Changes

• Because a datafile specification was not provided, the tablespace is Oracle managed. The datafile clause is only optional if the DB_CREATE_FILE_DEST initialization parameter is set. The parameter specifies an operating system directory that is the default storage location for Oracle managed datafiles. The operating system directory must already exist and must have the proper security permissions to allow Oracle to create files in it. If a datafile specification and SIZE parameter are not specified, a 100-megabyte file is created by default. During tablespace creation, the database server selects a file name for the Oracle managed file and creates the file in the directory specified in the db_create_file_dest initialization parameter. When the tablespace is dropped, Oracle automatically removes the Oracle managed files associated with the dropped tablespace. By default, an Oracle managed datafile is autoextensible with an unlimited maximum size.
   

• The tablespace will be locally managed because we did not specify EXTENT MANAGEMENT DICTIONARY during creation. Oracle has changed the default from dictionary managed in Oracle8i to locally managed in Oracle9i. Locally managed tablespaces track all extent information in the tablespace itself, using bitmaps. Tracking extents in bitmaps improves speed and concurrency of space operations.

Administrators are able to override Oracle managed extents by specifying EXTENT MANAGEMENT DICTIONARY in the tablespace definition. Dictionary managed tablespaces rely on data dictionary tables to track space utilization within the tablespace. The SYSTEM tablespace is always dictionary managed.
 

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