Extents in Oracle

An extent is a part of a segment. It consists of one or more contiguos db blocks.

Space for data on a harddisk is allocated in extents. An extent belongs to a tablespace.

One or more extents make a segment.

sys.fet$ and sys.uet$ maintaint free and used extents.

Thanks to Rahul Agarwal who improved this page.

Thanks also to Eliza who notified me of a type on this page.