Oracle database physical files

The files that constitute an Oracle database are organized into the following:

• Control files: Contain data about the database itself (that is, physical database structure
information). These files are critical to the database. Without them, you cannot open data
files to access the data within the database.

• Data files: Contain the user or application data of the database

• Online redo log files: Allow for instance recovery of the database. If the database crashes
and does not lose any data files, then the instance can recover the database with the
information in these files.

The following additional files are important to the successful running of the database:

• Parameter file: Is used to define how the instance is configured when it starts up

• Password file: Allows users to connect remotely to the database and perform
administrative tasks

• Backup files: Are used for database recovery. You typically restore a backup file when a
media failure or user error has damaged or deleted the original file.

• Archive log files: Contain an ongoing history of the data changes (redo) that are generated
by the instance. Using these files and a backup of the database, you can recover a lost data
file. That is, archive logs enable the recovery of restored data files.

• Trace files: Each server and background process can write to an associated trace file.
When an internal error is detected by a process, the process dumps information about the
error to its trace file. Some of the information written to a trace file is intended for the
database administrator, whereas other information is for Oracle Support Services.

• Alert log files: These are special trace files. They are also known as alert logs. The alert
log of a database is a chronological log of messages and errors. Oracle recommends that
you review these files.