Databases Reference
In-Depth Information
Instance
Memory structures
Background processes
Database
Physical
database
structure
Redo log
files
Datafiles
Control file
Datafile 1
Datafile 2
Datafile 3
Datafile 4
Datafile 5
Database
Logical
database
structure
SYSTEM
tablespace
SYSAUX
tablespace
Tablespace
1
Tablespace
2
Datafiles
The
in a database contain all of the database data that the users of
the database save and retrieve. A single datafile is an operating system file on the
server's disk. Each datafile belongs to only one tablespace; a tablespace can have
many datafiles associated with it.
There are five physical datafiles in the database in the physical structure
illustration: one is used for the
datafiles
datafiles
Files that contain all of the database
data that the users of the database save
and retrieve using
and other
DML statements. A tablespace com-
prises one or more datafiles.
SELECT
SYSTEM
tablespace, one is used for the
SYSAUX
tablespace, two datafiles are assigned to Tablespace 1, and the fifth datafile is
assigned to Tablespace 2.
Redo Log Files
The
facilitate the Oracle mechanism to recover from an instance
failure or a media failure. When any changes are made to the database, such as
updates to data or creating or dropping database objects, the changes are
recorded to the redo log files first. A database has at least two redo log files, and
it is recommended that multiple copies of the redo log files be stored on different
disks. (Oracle automatically keeps the multiple copies in synch.) If the instance
redo log files
redo log files
Files that contain a record of all changes
made to the data in both tables and
indexes as well as changes to the data-
base structures themselves. These files
are used to recover changed data that
was in memory at the time of a crash.
