Oracle Segments

In Oracle a Segment if defined as an entity that consumes physical storage space within the database. A Table is obviously one kind of segment, as is an Index.

Segments are made up of Extents. A Segment can have between one and two billion Extents.

Extents are made up of Oracle Database Blocks. The minimum size of an Extent is five Oracle Database Blocks.

Database Blocks are made up of one or more Operating System Blocks.

The structure for Oracle’s Segments looks like this:

        Segment
                Extent
                        Oracle Database Block
                                Operating System Block


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