Physical Files of Oracle Database

Control files, data files, redo log files, password file, parameter files, alert files, alert & trace files are the physical files of Oracle Database. I will discuss them one by one here.

Control Files

 Control files are in binary files. They contain information about the database. They are needed to mount the database. In the control files the following information contains:

i) Database Identifier

ii) Database Name

iii) Creation Date

iv)  The names and locations of the data files and redo log files

v) Table space information

vi) Log history, log sequence information, check point data and backup information.




The names and locations of the control files are kept in the parameter files of the database. The control files have the .ctl extension. As for example, the name of the control file can be control01.ctl
However, the database instance starts, control files are read to get back information of the database.

Data Files

The data files of a database amass data. Data files are related to a logical component of a database called Table Space. The table spaces are the logical structures of the database that keep data in form of segments.  

 The nature of table space can be permanent or of undo type. The table spaces which are temporary keep data temporary in nature that is created during sort operations. Undo table space amass data that is created to store the previous values of data that is manipulated. An oracle database has two data files which are mandatory- the files belonging to the SYSTEM  table space and the files belonging to the SYSAUX table space.

Redo Log Files

The online redo logs files lay up the details of all the changes that are performed against the database. The changes could be data manipulation, data definition or structural changes to the database. Every databse must have two redo logs. The Redo log files belong to a group. It is better to say that every data base must have a minimum of two redo groups with one member. The redo log files have the .log extension. The name of a redo log can be redo01.log.

Parameter Files

The oracle database has two types of parameter files such as Initialization Parameter File(pfile) and Server Parameter File(spfile). 

i) The pfile is a text file which can be opened, read and edited using a simple text editor.

ii) The spfile is a binary file that is updated by oracle software while making changes to initialization parameters. 

The parameter files are used for database startup and used to build up  the oracle instance and oracle database. It contains parameters and values. If both the pfile and spfile are available, the spfile is used to starting up the database. Typically the parameter files have .ora extension. As for example: 

i) unitorcl.ora and ii)spfileorcl.ora.

  Password File

The password file includes authentication information for an oracle database. It keeps the names and password of users possessing the SYSDBA or SYSOPER roles. These two are the the privileged roles. They give  a user the ability to perform administrative tasks in the database - Start up, shutdown etc. This Password File is a binary file and optional.