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Oracle Backup and Recovery Enhancements

Oracle Tips by Burleson Consulting

This is an excerpt from "Oracle 10g New Features for Administrators" by Ahmed Baraka.

Using the Flash Recovery Area

The flash recovery area serves as the default storage area for all files related to backup and restore operations.

The flash recovery area provides the following benefits:

• Single storage location for all recovery-related files.

• Automatic management of recovery-related disk space.

• Faster backup and restore operations, since you don’t need to restore tape   backups.

• Increased reliability of backups, since disks are generally safer storage   devices than tapes.

What’s in the Flash Recovery Area?

The flash recovery area may contain the following files:

Datafile copies: The new RMAN command BACKUP AS COPY can be used to create image copies of all datafiles and automatically store in the flash recovery area.

Control file autobackups: The database places any control file backups it generates in the flash recovery area.

Archived redo log files: If you store Archived redo log files in the flash recovery area, Oracle will automatically delete the files.

Online redo log files: Oracle recommends that you save a multiplexed copy of your online redo log files in the flash recovery area. The following statements can create online redo logs in the flash recovery area:

CREATE DATABASE, ALTER DATABASE ADD LOGFILE, ALTER DATABASE ADD STANDBY LOGFILE, and ALTER DATABASE OPEN RESETLOGS.

Current control files: Oracle also recommends that you store a multiplexed current control file in the flash recovery area.

RMAN files

Flashback logs: If you enable the flashback database feature, Oracle copies images of each altered block in every datafile into flashback logs stored in the flash recovery area.

Note: Oracle calls the multiplexed redo log files and control files in the flash recovery area permanent files, since they should never be deleted and are part of the live database. Oracle terms all the other files in the flash recovery area (recovery related files) transient files, since Oracle will delete them eventually after they have become obsolete or have already been copied to tape.

Creating a Flash Recovery Area

You use the DB_RECOVERY_FILE_DEST and  DB_RECOVERY_FILE_DEST_SIZE initialization parameters to configure a flash recovery area in your database.

When you use the DB_RECOVERY_FILE_DEST parameter to specify the destination of your flash recovery area, you can use a directory, file system, or ASM disk group as your destination. 

Dynamically Defining the Flash Recovery Area

ALTER SYSTEM SET DB_RECOVERY_FILE_DEST_SIZE =
2G SCOPE=BOTH
ALTER SYSTEM SET DB_RECOVERY_FILE_DEST =
'C:\ORACLE\RECOVERY_AREA' SCOPE=BOTH


You must always specify the size parameter before specifying the location parameter.

Disabling the Current Flash Recovery Area

ALTER SYSTEM SET DB_RECOVERY_FILE_DEST = ''

Note: even after you disable the flash recovery area, the RMAN will continue to access the files located in the flash recovery area for backup and recovery purposes.

Default File Location and the Flash Recovery Area

The initialization parameters DB_CREATE_FILE_DEST and DB_CREATE_ONLINE_LOG_DEST_n determine the location of all OMF files.

Control Files

If you haven’t set the CONTROL_FILES parameter, Oracle will create the control files in various default locations, according to the following rules:

• If you specify the DB_CREATE_ONLINE_LOG_DEST_n parameter, Oracle will create an OMF-based control file in n number of locations, with the first directory holding the primary control file.

• If you specify the DB_CREATE_FILE_DEST and DB_RECOVERY_FILE_DEST parameters, Oracle will create an OMF based control file in both of these locations.

• If you just specify the DB_RECOVERY_FILE_DEST parameter, Oracle will create an OMF-based control file in the flash recovery area only.

• If you omit all three of the initialization parameters, Oracle will create a non-OMF-based control file in the system-specific default location.

Note: If the database creates an OMF control file, and it is using a server parameter file, then the database sets the CONTROL_FILES initialization parameter in the server parameter file.

Redo Log Files

If you omit the LOGFILE clause during database creation, Oracle will create the redo log files according to the same rules as mentioned above.

 

If you like Oracle tuning, see the book "Oracle Tuning: The Definitive Reference", with 950 pages of tuning tips and scripts. 

You can buy it direct from the publisher for 30%-off and get instant access to the code depot of Oracle tuning scripts.


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