1-21. Segments

• Data segments: Each nonclustered, non-indexed-organized table has a data segment. All of the table's data is stored in the extents of its data segment. For a partitioned table, each partition has a data segment. Each cluster has a data segment. The data of every table in the cluster is stored in the cluster's data segment.
• Index segments: each index has an index segment that stores all of its data. For a partitioned index. each partition has an index segment.
• Undo segments: one UNDO tablespace is created by the database administrator to temporarily store undo information. This information in an undo segment is used to generate read-consistent database information and, during database recovery, to roll back uncommitted transactions for users.
• Temporary segments: Temporary segments are created by the Oracle database when a SQL statement needs a temporary work area to complete execution. When the statement finishes execution, the temporary segment's extents are returned to the instance for future use. Specify a default temporary tablespace for every user or a default temporary tablespace, which is used databasewide.