Apress.Expert.Oracle.Database.Architecture.9i.and.10g.Programming.Techniques.and.Solutions.Sep.2005

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CHAPTER 3 ■ FILES
To use this feature, the database must be in ARCHIVELOG mode and must have been set up
to enable the FLASHBACK DATABASE command. What I’m trying to say is that you need to have
set up this capability prior to having a need to use it. It is not something you can enable after
the damage is done; you must make a conscious decision to use it.
Flash Recovery Area
The Flash Recovery Area is a new concept in Oracle 10g. For the first time in many years (over
25 years), the basic concept behind database backups has changed in Oracle. In the past, the
design of backup and recovery in the database was built around the concept of a sequential
medium, such as a tape device. That is, random access devices (disk drives) were always considered
too expensive to waste for mere backups. You used relatively inexpensive tape devices
with large storage capacities.
Today, however, you can buy terabytes of disk storage at a very low cost. In fact, by 2007,
HP intends to ship desktop computers with terabyte disk drives. I remember my first hard drive
on my personal computer: a whopping 40MB. I actually had to partition it into two logical
disks because the OS I was using (MS-DOS at the time) could not recognize a disk larger than
32MB. Things have certainly changed in the last 20 years.
The Flash Recovery Area in Oracle 10g is a new location where Oracle will manage many
of the files related to database backup and recovery. In this area (an area being a set-aside area
of disk for this purpose; a directory, for example), you could find
• Copies of data files on disk
• Incremental backups of your database
• Redo logs (archived redo logs)
• Control files and backups of control files
• Flashback logs
This new area is used to allow Oracle to manage these files, for the server to have knowledge
of what is on disk and what is not on disk (and perhaps on tape elsewhere). Using this
information, the database can perform operations like a disk-to-disk restore of a damaged
data file or the flashing back (a “rewind” operation) of the database to undo an operation that
should not have taken place. For example, you could use the flashback database command
to put the database back the way it was five minutes ago (without doing a full restore of the
database and a point in time recovery). That would allow you to “undrop” that accidentally
dropped user account.
The Flash Recovery Area is more of a “logical” concept. It is a holding area for the file
types discussed in this chapter. Its use is optional—you do not need to use it—but if you want
to use some advanced features such as the Flashback Database, you must use this area to store
the information.
DMP Files (EXP/IMP Files)
Export and Import are venerable Oracle data extraction and load tools that have been around
for many versions. Export’s job is to create a platform-independent DMP file that contains all