Overview of Physical Database Structures : 1

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                The data of logical database structures, such as tables and indexes, is

physically stored in the datafiles allocated for a database.

Datafiles have the following characteristics:

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One or more datafiles form a logical unit of database storage called a tablespace.

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A datafile can be associated with only one tablespace.

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Data in a datafile is read, as needed, during normal database operation and stored in

the memory cache of Oracle Database. For example, if a user wants to access some

data in a table of a database, and if the requested information is not already in the

memory cache for the database, then it is read from the appropriate datafiles and

stored in memory.
Datafiles can be defined to extend automatically when they are full.

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A control file contains entries that specify the

physical structure of the database, including the following information:

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Database name

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Names and locations of datafiles and redo log files

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Oracle Database can

number of identical control file copies, to protect against a failure involving the control

file.

Every time an

datafiles, tempfiles, and redo log files that must be opened for database operation to

proceed.
Timestamp of database creationmultiplex the control file, that is, simultaneously maintain ainstance of an Oracle database is started, its control file identifies the

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These online

redo log files, together with archived copies of redo log files, are collectively known as

the redo log for the database. A

records

from being permanently written to the datafiles, then the changes can be obtained

from the redo log, so work is never lost.
redo log is made up of redo entries (also called redo), which record all changes made to data. If a failure prevents modified data■
            Archived redo log files are database-generated offline copies of online redo log files.

ARCHIVELOG

online redo log.mode. Oracle recommends that you enable automatic archiving of the

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

database. Both parameter files (pfiles) and server parameter files (spfiles) let you store

and manage your initialization parameters persistently in a server-side disk file. A

server parameter file has these additional advantages:

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active instance.

The file is concurrently updated when some parameter values are changed in the

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database.

Oracle recommends that you create a server parameter file as a dynamic means of

maintaining initialization parameters.
The file is centrally located for access by all instance in a Real Application Services

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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, while other information is for Oracle Support Services. Trace

file information is also used to tune applications and instances. The alert file, or alert

log, is a special trace file. The alert log of a database is a chronological log of messages

and errors.
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To restore a file is to replace it with a backup file. Typically, you restore a file when a

media failure or user error has damaged or deleted the original file.

User-managed backup and recovery requires you to actually restore backup files

before you can perform a trial recovery of the backups.

Server-managed backup and recovery manages the backup process, such as

scheduling of backups, as well as the recovery process, such as applying the correct

backup file when recovery is needed.Backup FilesAlert and Trace Log FilesParameter Files

Oracle Database automatically archives redo log files when the database is in

Archived Redo Log FilesOnline Redo Log FilesControl FilesDatafiles