Database Storage Structures Logical structures such as tablespaces are created and recognized by the database only. It is unknown to OS. Physical structures are those that can seen and operated on from the OS, such as the physical files that store data on disk Recovery related structures such as redo logs and database backups are used to recover the database after an OS failure, Oracle Instance failure, or media failure. CS5614 Database Management Systems VirginiaTech

CS5614 Database Management Systems VirginiaTech

Tablespace The logical structure of the database consists of tablespace, segments and extents. Tablespace is an area where Oracle places new objects. A tablespace is a logical group of one or more physical datafiles or tempfiles. Database contains one or more tablespaces. CS5614 Database Management Systems VirginiaTech

Blocks, Extents & Segments The units of database space allocation are data blocks, extents, and segments Block: At the finest level of granularity, Oracle stores data in data blocks. Extent: An extent is a specified number of contiguous data blocks allocated for storing a specific type of information Segment: A segment is a set of extents, each of which has been allocated for a specific data structure. Each table data is stored in its own segment. CS5614 Database Management Systems VirginiaTech

Blocks, Extents, and Segments CS5614 Database Management Systems VirginiaTech

PCTFREE & PCTUSED CS5614 Database Management Systems VirginiaTech

Types of tablespaces Permanent tablespaces: These tablespaces are used to store system and user data. Eg: USERS, SYSTEM Temporary tablespaces: These tablespaces improves the concurrency of multiple sort operations, and reduce their overhead. Eg: sorting, grouping Undo tablespace: Oracle database creates and manages undo data in this tablespace. Undo data: Oracle makes a copy of the original data before modifying it. The original copy is called undo data CS5614 Database Management Systems VirginiaTech

Physical structures Datafiles: These are the OS files that hold database data. The data is written to these files in a Oracle-proprietary format that cannot be read by programs other than Oracle database. Tempfiles:These are the special class of datafiles that are associated with temporary tablespaces. Control file is a binary file that keeps track of all the files' Oracle needs and where they are on the host machine. CS5614 Database Management Systems VirginiaTech

Physical structures (continued)‏ Server parameter file: This file contains all initialization parameters that Oracle Database uses. Password file: used to authenticate a user who is logging in remotely as user SYS. CS5614 Database Management Systems VirginiaTech

CS5614 Database Management Systems VirginiaTech

References Oracle® Database Express Edition 2 Day DBA 10g Release 2 (10.2)‏ Oracle Database Adminstrator's reference 10g Release (10.1)‏ http://www.oracle.com/technology/documentation/database10g.html http://www.stanford.edu/dept/itss/docs/oracle/10g/server.101/b10739/ tspaces.htm#i1006157 http://download.oracle.com/docs/cd/B28359_01/server.111/b28310/o nlineredo001.htm http://download.oracle.com/docs/cd/B19306_01/server.102/b14220/lo gical.htm CS5614 Database Management Systems VirginiaTech