Files - Expert Oracle Database Architecture - page 121

The Fast Recovery Area in Oracle is a location where the database will manage many of the files related to
database backup and recovery. In this area (an area being a part of a disk set aside for this purpose; a directory, for
example), you could find the following:

• RMAN backup pieces (full and/or incremental backups)

• RMAN image copies (byte-for-byte copies of data files and control files)

• Online redo logs

• Archived redo logs

• Multiplexed control files

• Flashback logs

Oracle uses this new area to manage these files, so the server will know 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 Fast 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 don't 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 of the required metadata (in the form of
CREATE and ALTER statements), and optionally the data itself to re-create tables, schemas, or even entire databases.
Import's sole job is to read these DMP files, and execute the DDL statements and load any data it finds.

■ export is officially deprecated with Oracle 11 g release 2. it is supplied only for use with legacy database
structures. New data types, new structures, new database features will not be supported by this tool. i strongly
recommend using Data Pump , the export/import replacement tool introduced with Oracle 10 g several years back.

Note

DMP files are designed to be forward-compatible, meaning that newer releases can read older releases' DMP
files and process them successfully. I have heard of people exporting a version 5 database and successfully importing
it into Oracle 10 g (just as a test). So Import can read older version DMP files and process the data therein. The
converse, however, is most definitely not true: the Import process that comes with Oracle9 i Release 1 can't—will
not—successfully read a DMP file created by Oracle9 i Release 2 or Oracle 10 g Release 1. For example, I exported a
simple table from Oracle 11 g Release 2. Upon trying to use these DMP files in Oracle 10 g Release 2, I soon discovered
Oracle 10 g Release 2 Import will not even attempt to process the Oracle 11 g Release 2 DMP file:

$ imp userid=/ full=y

Import: Release 10.2.0.4.0 - Production on Wed Jan 20 18:21:03 2010

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