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Oracle Database Data Blocks
At the finest level of granularity, Oracle Database data
is stored in data blocks.
One data block corresponds to a specific number of
bytes of physical database space on disk.
The standard block size is specified by the
DB_BLOCK_SIZE initialization parameter.
A database uses and allocates free database space in
Oracle Database data blocks.
Extents
The next level of logical database space is an extent.
An extent is a specific number of contiguous data
blocks, obtained in a single allocation, used to store a
specific type of information.
Segments
Above extents, the level of logical database storage is a
segment.
A segment is a set of extents allocated for a table, index,
rollback segment, or for temporary use by a session,
transaction, or SQL parser.
In relation to physical database structures, all extents belonging
to a segment exist in the same tablespace, but they may be in
different data files.
When the extents of a segment are full, Oracle Database
dynamically allocates another extent for that segment.
Segments Cont’d
Data segment – stores table data
Index segment – stores index data
Temporary segment – temporary space used
during SQL execution
Rollback Segment – stores undo
Oracle Database Data Blocks
At the finest level of granularity, Oracle Database data is stored in data blocks.
One data block corresponds to a specific number of bytes of physical database space on disk.
The standard block size is specified by the DB_BLOCK_SIZE initialization parameter.
A database uses and allocates free database space in Oracle Database data blocks.
Extents
The next level of logical database space is an extent. An extent is a specific number of contiguous data blocks, obtained in a single allocation, used to store a specific type of information.
Segments
Above extents, the level of logical database storage is a segment.
A segment is a set of extents allocated for a table, index, rollback segment, or for temporary use by a session, transaction, or SQL parser.
In relation to physical database structures, all extents belonging to a segment exist in the same tablespace, but they may be in different data files.
When the extents of a segment are full, Oracle Database dynamically allocates another extent for that segment.
Segments Cont’d
Data segment – stores table data
Index segment – stores index data
Temporary segment – temporary space used during SQL execution
Rollback Segment – stores undo
False
