CS5614 Database Management Systems VirginiaTech1 Database Storage Structures Logical structures such...
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Transcript of CS5614 Database Management Systems VirginiaTech1 Database Storage Structures Logical structures such...
CS5614 Database Management Systems
VirginiaTech 1
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 2
CS5614 Database Management Systems
VirginiaTech 3
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.
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Blocks, Extents & SegmentsThe 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.
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Blocks, Extents, and Segments
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PCTFREE & PCTUSED
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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
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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.
Physical structures
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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.
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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/onlineredo001.htm
http://download.oracle.com/docs/cd/B19306_01/server.102/b14220/logical.htm