Space Management in Tablespaces

Locally Managed Tablespaces

1. Free Extent Information is NOT stored in Data Dictionary
2. Bitmap Segments are used to keep track of the free space usage
3. Within the tablespace, there are bitmap segments
4. Each bit in the Bitmap corresponds to a Data Block or a group of Data Blocks and the value in the bit indicates that the blocks are free or used
5. Whenever a block is used or freed for reuse, Oracle changes the value of the bitmap to show the new status of the block
6. Contention is significantly reduced on the data dictionary tables
7. Coalescing of free space is NOT required

Dictionary Managed Tablespaces

1. This is the default method for the creation of tablespace
2. Free Extent Information is stored in Data Dictionary
3. Contention is significantly INCREASED on the data dictionary tables
4. Oracle updates the appropriate tables in the data dictionary whenever an extent is allocated or deallocated in relation to the tablespace
5. Coalescing is required in frequently updated segments in Dictionary Managed Tablespaces

 

To indicate the Space Management during the creation of a Tablespace, EXTENT MANAGEMENT clause needs to be specified as follows:

EXTENT_MANAGEMENT [DICTIONARY | LOCAL [AUTOALLOCATE | UNIFORM [SIZE integer [K|M]]]

 

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