RGPV DBMS Questions

Define Segment, Extent and Block?
(RGPV Dec 2014,Dec 2010, Dec 2009)
Sol.

Block: A database block is the smallest unit of storage in Oracle.
Oracle manages the storage space in the datafiles of its database in these units.
The size of block is a specific number of bytes of storage within a given tablespace.
The default block size is specified by the Oracle initialization parameter that is DB_BLOCK_SIZE.

Extent: An extent is the next level of logical grouping in the database. An extent consist of one or more database blocks. When we enlarge a database object, the spece added to the object is allocated as an extent.

Segment: Segment is a group of extents that form a database object that oracle treats as a unit, such as table.
There are four types of segments-
  1. Data segment – It is a storage part.
  2. Index segment – Its hold all of its data.
  3. Temporary segment – It’s a temporary work space.
  4. Undo segment – to do transaction undo




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