Performing Oracle User-Managed Backups - OCP: Oracle Database 12c Administrator Certified Professional - page 17

NOARCHIVELOG and ARCHIVELOG Modes
Oracle Database runs in two principal modes, NOARCHIVELOG (the default) and
ARCHIVELOG. The logging bit has to do with archived redo logs and if they are saved or
not, which makes a difference in the kinds of recoveries that you can do. Let's look at each
mode in a bit more detail.
For manual backup and recovery questions in the OCP exam you will only
have to be concerned with databases in NOARCHIVELOG mode. When you
are asked RMAN questions you may be asked about either ARCHIVELOG
mode or NOARCHIVELOG mode. So we cover both modes here.
NOARCHIVELOG MODE
NOARCHIVELOG mode is the default logging mode. In NOARCHIVELOG mode, the
online redo logs are overwritten over time and no backups are created. Because of this, you
are limited in the way you can back up your database and how you can recover it.
Backups are limited to cold or offline backups. This means that you must shut down your
database before you can back it up. As you will see in later sections of this chapter, you will
back up all the data files of the database plus the online redo logs and the control file(s).
Recovery in NOARCHIVELOG is equally limited. In NOARCHIVELOG mode, you
can restore the database only to the point in time that the backup was taken. Thus you will
lose any changes to the database that took place after the backup was complete and the
database was opened for business. This is typically not an acceptable solution for produc-
tion databases.
We will discuss how to back up your database in NOARCHIVELOG mode later in this
chapter. In Chapter 2, “Performing Oracle User-Managed Database Recoveries,” we will dis-
cuss recovering your database with backups taken in NOARCHIVELOG mode. In Chapter 3
we will discuss using RMAN to perform offline backups, and in Chapter 5, “Recovering
Databases with RMAN,” we will discuss using RMAN to restore these backups.
ARCHIVELOG MODE
ARCHIVELOG mode is a much more flexible method of operating your database and is
strongly recommended for all production databases. In this mode, you can back up your
database while it's up and running, allowing users to work at the same time that the back-
ups are running.
When the database is in ARCHIVELOG mode, changes are recorded in the online
redo logs as usual. What is different is that the archived redo logs are copied to a backup
directory once they have filled up. These copies of the redo log files are called archived
redo logs and the Oracle Database process that copies them is called the ARCH process .
In Oracle Database 12 c , the ARC n process starts automatically when the database is in
ARCHIVELOG mode.