Extent Management: Locally Managed

A tablespace that manages its own extents, maintains a bitmap in each data file to keep track of the free, or used status of blocks in that data file. Each bit in the bitmap corresponds to a block, or a group of blocks. When an extent is allocated or freed for reuse, Oracle changes the bitmap values to show the new status of the blocks. These changes do not generate rollback information because they do not update tables in the data dictionary (except for special cases such as tablespace quota information).

Locally-managed tablespaces have the following advantages over dictionary-managed tablespaces:

Local management of extents avoids recursive space management operations, which can occur in dictionary -managed tablespaces if consuming or releasing space in an extent results in another operation that consumes or releases space in a rollback segment or data dictionary table.
Local management of extents automatically tracks adjacent free space, eliminating the need to coalesce free extents.
The sizes of extents that are managed locally can be determined automatically by the system. Alternatively, all extents can have the same size in a locally -managed tablespace.

Extent Management: Locally Managed

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