Oracle Flash recovery area)

It has been several years since the Oracle flash back zone was launched at 10 GB and continues until now. Oracle flash back is prepared for RMAN. Although aside from it, we can also perform database backup and recovery, Oracle is strongly recommended to use it and make it one of RMAN components. This is because the region can centrally simplify management and Backup recovery, which is also attractive. This article describes the features of the Oracle flash back area, its configuration flash back area, and monitoring flash back area.

1. Flash back zone features and Configuration

Flash back area
It is to allocate a specific directory location (a directory on a general disk or an ASM disk) to store specific recovery files for centralized and simplified management of database recovery.
By configuring the flash back area, you can avoid affecting the situation of all instances when the disk space is exhausted when multiple instances are archived to the same disk. That is to say, narrow the impact scope.
The abbreviation of the flash back area is FRA. The following description indicates the flash back area. It may also be mixed with the flash back area or FRA.
 
Types of files that can be stored in the flash back area
Full data file backup
Incremental Backup
Data file copy
Current Control File, backup control file, spfile file, snapshot Control File
Online log files and archived logs
Block tracking files and flash logs

Enable and disable the flash back area
Set the following initialization parameters (spfile or pfile file)
DB_RECOVERY_FILE_DEST_SIZE: used to set the size of the flash back area, this parameter should be prior to the DB_RECOVERY_FILE_DEST parameter modification, otherwise the ORA-32001
DB_RECOVERY_FILE_DEST: directory used to set the flash back area
DB_FLASHBACK_RETENTION_TARGET: specifies the time range for the database to flash back. The unit is minute. The default value is 1440 minutes, that is, one day.
Database flash back is divided into multiple situations. The flash back log is stored in FRA, and the time to flash back also depends on the size of the flash back recovery zone.
Set DB_RECOVERY_FILE_DEST to null. FRA can be disabled. However, if flashback database is enabled, FRA cannot be canceled. You must first disable flashback database.
 
Database FRA can configure different flash back zones for each database, or configure flash back zones with the same path for multiple databases.
When you configure the same location for multiple databases, consider the total size of the disk mount point where the flash back area is located and use different DB_NAME
When multiple databases or instances use the same flash back area, the path is: FRA_HOME/<db_name>/<file_type>/<date>/<file_name>

Retention Policy in FRA
The retention of files in FRA is determined by the RMAN retention policy. Execute the RMAN configure retention policy command to set its policy
Files that are not associated with a retention policy or are permanently stored will never be deleted.
Files associated with the retention policy will not be deleted if they are not out of date. Once they are out of date, they will be automatically deleted under the pressure of space.

FRA and multi-path log Archiving
If the archive log parameter log_archive_dest_n is set, this location is used instead of FRA.
If the log_archive_dest_n parameter is not set but FRA is enabled, you do not need to set the archive log parameter log_archive_dest_n separately.
After FRA is enabled, log_archive_dest and log_archive_duplex_dest cannot be set, that is, exclusive mode exists. See Oracle archiving logs.
To archive the file to log_archive_dest_n and FRA, you must set the log_archive_dest_10 parameter to FRA, as shown below:
Alter system set log_archive_dest_10 = 'location = USE_DB_RECOVERY_FILE_DEST ';
Alter system set log_archive_dest_1 = 'location =/u03/database/archdir ';

2. FRA space allocation and monitoring
After the FRA feature is enabled, FRA helps you manage all disk space allocations. Oracle automatically monitors FRA space usage.
For FRA space allocation, consider the current database backup method, whether the backup is compressed, the log size archived every day, whether flash back is enabled, and other factors.
If the available space in FRA is unsafe or insufficient, you can obtain relevant information through OEM or DBA_OUTSTANDING_ALERTS.
A warning is generated in the Alert Log File.
Generates an alert when the reclaimed space is less than 15% of the value defined by DB_RECOVERY_FILE_DEST_SIZE.
Generates a severe alarm when the reclaimed space is less than 3% of the value defined by DB_RECOVERY_FILE_DEST_SIZE.
When the entire FRA is fully filled, the system is not available, giving you ORA-19815, ORA-19809: limit exceeded for recovery files
NOTE: If FRA space is filled up, it does not indicate that the current disk mount point space is insufficient.

If FRA space is insufficient or serious alarms occur, consider solving the problem from the following aspects:
If only the size limit of the parameter DB_RECOVERY_FILE_DEST_SIZE is exceeded, the parameter is directly modified to a larger value.
If there is not much free space on the disk, allocate more disk space to the file system, and then modify the DB_RECOVERY_FILE_DEST_SIZE parameter to a larger value.
If you cannot allocate additional disk space, consider migrating FRA to another file system with more available space.
You can use the backup recovery area command to move the entire FRA content to another location.
Delete an earlier backup set or archive log in FRA. We recommend that you use the RMAN command to delete the backup set or archive log. If you delete the backup set directly from the OS, Oracle considers that the FRA space has not been released (crosscheck is required and then delete)
-- Author: Leshami
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