1. ISYS366, Oracle Disk Internals
4/30/2019
ISYS366, Oracle Disk Internals

2. Oracle Database Structures
Tablespace
Logical, because the physical implementation is the datafile.
Corresponds not only to one or more tables but also to one or more datafiles.
BUT, a table cannot span more than one tablespace.
SYSTEM is the first tablespace. Holds data dictionary.
Can be taken off line or dropped (except SYSTEM).
4/30/2019

3. Oracle Database Structures
CREATE TABLESPACE tablespace_name DATAFILE datafile_name …
A word about raw files
UNIX and NT
Eliminates OS I/O
Backup Issues
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4. Creating a Tablespace: Example
Create Tablespace bigtbs_01 Datafile ‘bigtbs_f1.dat’ Size 20M AUTOEXTEND ON;
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5. Oracle Database Structures
Segments: A unit of logical storage
One or more segments = Tablespace
Data segments
holds table data
one per table
Rollback segments
holds information used to make rollbacks
Index segment
holds data used in indexes
Temporary segment
used for executing certain SQL operations, such as sorting, that cannot be performed in memory
4/30/2019

6. Oracle Database Structures
Extents
One or more extents = Segment
Data blocks
One or more data blocks = Extent
Size depends on operating system for a default (may be overridden by changing DB_BLOCK_SIZE in INITX.ORA)
4/30/2019

7. Oracle Database Structures
Data blocks
Contains
Row data
Free space
Block information: block address (in datafile), segment
Type, tables and rows that use the block and other header information
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8. Oracle Database Structures
Datafiles
Operating system files
One or more per tablespace
Datafile = is made up of segments
Redo logfiles
Restore the database to last physical backup
Restore the database to point in time of failure (must be running in ARCHIVELOG mode)
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9. Oracle Database Structures
Initialization Parameter File (INIT<SID>.ORA)
D:\orawin\database\initorcl.ora
Only read at startup time
One per instance
4/30/2019