Oracle Database - (Logical) Segment (Database Object Storage)

About

A segment is a logical storage structure that contains data structure (segment type) of database objects.

For example:

• each table's data is stored in its own data segment,
• while each index's data is stored in its own index segment.

One segment name is one object but one object may have several segments records.

A segment is uniquely defined with the following columns:

• the owner
• the segment name
• the partition name (A table may have several partitions)
• the segment type (A package has a body and a definition)

A segment is an set (unordered) of extents. A segment and all its extents are stored in one tablespace.

Oracle Database allocates space for segments in units of one extent. When the existing extents of a segment are full, Oracle Database allocates another extent for that segment. Because extents are allocated as needed, the extents of a segment may or may not be contiguous on disk.

Within a tablespace, a segment can include extents from more than one file; that is, the segment can span datafiles.

Articles Related

Type

Data Structure (Segment Type)

• CACHE
• CLUSTER
• DEFERRED ROLLBACK
• INDEX (An index)
• INDEX PARTITION (An index partitioned)
• INDEX SUBPARTITION (An index subpartition)
• LOBINDEX (Index of LOB column)
• LOBSEGMENT (Content of a LOB column)
• LOB PARTITION (Content of lob column in a partitioned table)
• LOB SUBPARTITION (Content of lob column in a subpartition)
• NESTED TABLE (A nested-table content)
• ROLLBACK
• SPACE HEADER
• TABLE (A table content)
• TABLE PARTITION (A table partition content)
• TABLE SUBPARTITION (A table sub-partition content)
• TEMPORARY
• TYPE2 UNDO
• UNDEFINED