Logical Storage Structure (LSS)
- Oracle database allocates logical space for all data in the database.
- The logical units of database space allocation are Data blocks, Extents, Segments, Tablespace.
- Logical storage structure are created and recognized by oracle database and are not know to the operating system.
- At the physical level the data is stored in the data files on disk. The data in the data file is storage in operating system blocks.
Data block
Smallest logical unit of data storage is oracle database. One logical block corresponds to a specific number of bytes of physical disk space.
Extent
Extent is set of logically continuous data block allocated for storing a specific type of information.
Ex (collection of data block is nothing but extent. Means 100 datablock is one extent)
Segment
Segment is set of extent allocated for a specific database object, such a table.
Ex (collection of segment is called as segment)
Tablespace
It is a database storage unit that contains one or more segments
Ex (collection of segment )