Performing Oracle User-Managed Backups - OCP: Oracle Database 12c Administrator Certified Professional - page 12

Oracle Data Files
The Oracle Database data files are critical database physical files that are used to store all
your Oracle data (well, almost all!). The physical data files are the structures most likely to
be lost and subsequently recovered during a database-recovery operation. You are probably
aware that database data files are preallocated in size and that they can be configured to
grow automatically.
When you perform a physical backup of your database, the database data files will be the
principle structures you back up. When you restore your database due to a media failure, you
will be restoring one or more data files. You may also have to restore other database files such
as the control file, the online redo logs, and the archived redo logs, which we will discuss later
in this section.
Another type of database backup is called a logical backup. We will discuss
logical backups in future chapters.
Data files can be in two different states. They can be online (the default) or offline. Some
Oracle database restore operations will require that you take one or more data files offline.
Oracle Tablespaces
A tablespace is a logical, named entity in the database that is used to store database objects.
For example, your database might have a table called STORES that contains data about stores
in your organization. The table STORES will be assigned to a tablespace, perhaps called
STORE_DATA .
A tablespace is assigned to one or more database data files, and the size of the tablespace
is related to the size of the underlying database data files. Several recovery options exist with
respect to tablespaces, including tablespace point-in-time recovery, which we will discuss in
later chapters of this topic.
Tablespaces can be in four different states. They can be online (the default), offline,
read-write (the default), or read-only. If you put your tablespace in read-only mode, then
you will need to back up the data files associated with that tablespace only once as long
as the tablespace is in read-only mode. Some recovery operations require the database be
offline to perform restore and recovery operations.
Redo Logs
The redo logs of the database are the principle vehicle for backup and recovery. In the
following sections, we will cover two different types of redo logs. First, we will discuss
the online redo log, and then we will discuss the archived redo log.
Online Redo Logs
Online redo logs are used by Oracle to store all the changes that occur in the database.
Think of them as something akin to a videotape recording of everything that is going on.