ORACLE Physical Database Structures

Datafiles

Every Oracle database has one or more physical datafiles.
The datafiles contain all the database data.
The data of logical database structures, such as tables and
indexes, is physically stored in the datafiles allocated for a
database.

Control Files

Every Oracle database has a control file. A control file contains
entries that specify the physical structure of the database.
For example, it contains the following information:


Database name

Names and locations of datafiles and redo log files

Time stamp of database creation


Redo Log Files

Every Oracle database has a set of two or more redo log files.
The set of redo log files is collectively known as the redo log
for the database. A redo log is made up of redo entries (also called
redo records).
The primary function of the redo log is to record all changes made
to data. If a failure prevents modified data from being permanently
written to the datafiles, then the changes can be obtained from the
redo log, so work is never lost.

Archive Log Files

You can enable automatic archiving of the redo log. Oracle
automatically archives log files when the database is in ARCHIVELOG mode.

Parameter Files

Parameter files contain a list of configuration parameters for
that instance and database.