Configuring the environment for RMAN backups_ Configure backup optimization

function RMAN Of CONFIGURE Command to enable and disable backup optimization . Backup optimization in some cases Skip file backup if the equivalent file or the equivalent version of the file has been backed up .

1． Overview of backup optimization

When backup optimization is enabled , If the equivalent file has been backed up to the specified device type ,BACKUP The command skips backing up files .

The following table describes RMAN A standard used to determine whether a file is equivalent to a backed up file .

file type	Confirm the standards of equivalent documents
Data files	The data file must have the same... As the data file in the backup DBID, checkpoint SCN, establish SCN,RESETLOGS SCN And time . Data files must be offline normally （offline-normal）, read-only , Or normally closed .
Archive log	same DBID, Threads , Serial number ,RESETLOGS SCN And time .
Backup set	same DBID, Backup set records ID And time stamp .

If RMAN Confirm that a file is equivalent to that it has been backed up , So it's a skipped candidate .RMAN Further checks must be made to confirm whether the file is skipped , However , The retention policy and backup two-way reuse feature are used to determine RMAN Whether there are enough backup algorithm elements on the specified device type .

If the above conditions are met ,RMAN Optimize with backup ：
1） command CONFIGURE BACKUP OPTIMIZATION ON Has been run to enable backup optimization
2） function BACKUP DATABASE,BACKUP ARCHIVELOG and ALL or LIKE Options , or BACKUP BACKUPSET ALL,BACKUP RECOVERY AREA,BACKUP RECOVERY FILES or BACKUP DATAFILECOPY.
notes ： When TO DESTINATION And BACKUP RECOVERY AREA or BACKUP RECOVERY FILE When used together ,RMAN Just skip backup TO DESTINATION There is an equivalent backup file in the location .
3） Only one channel type is assigned , Not in the same BACKUP Mixed disk and... On the command SBT passageway .

notes ： In backup undo Optimization ,RMAN Exclude committed transactions undo change （ Restoring a backup does not require ）. Backup optimization can be enabled and disabled , But backup undo Optimization is a built-in behavior .

for example , Suppose you have configured backup optimization . These commands back up the database , All archived logs and all backup sets to tape .
BACKUP DEVICE TYPE sbt DATABASE PLUS ARCHIVELOG;
BACKUP DEVICE TYPE sbt BACKUPSET ALL;

If a file that has not been backed up since the last backup has been changed , that RMAN The files will not be backed up again . If the file has been backed up ,RMAN Skip all files specified by the command ,RMAN It will also prompt errors .

Can be specified at any time BACKUP Ordered FORCE Option to undo the optimization . for example , Can run ：
BACKUP DATABASE FORCE;
BACKUP ARCHIVELOG ALL FORCE;

2．SBT Backup optimization effect of backup retention policy

When backing up to SBT Equipment time , Backup optimization is not always applied .

The behavior of normal backup optimization exceptions based on recovery windows and redundancy retention policies is described in the following sections .

notes ： If you use the media manager and its own internal expiration policy , Carefully enable backup optimization . Regular operation CROSSCHECK Command to synchronize with the media manager RMAN Restore directory . otherwise ,RMAN Skip backup due to optimization , Without realizing that the media manager has discarded the backup stored on tape .

2.1. SBT Backup recovery window for backup backup optimization of retention policy

Assume that the backup retention policy is in effect with backup optimization and recovery windows enabled . In this case , When executed SBT When the backup ,RMAN Always back up their most recent backup data files that are older than the recovery window .

for example , Suppose the following scenario ：
1） It's today 2 month 21 Japan
2） The recovery window is 7 God
3） Recent tablespaces tools Tape backup of is 1 month 3 Japan
4） Table space tools It's read-only

stay 2 month 21 Japan , When executing commands to back up tablespaces tools When to tape ,RMAN Back it up even if it is 1 month 3 No changes have been made since the backup of （ Because it's read-only ）.RMAN It is backed up because the tablespace is backed up in the 7 The recovery window period of days does not exist .

This behavior allows media management to set the old tape to expire . otherwise , The media manager is forced to remain indefinitely 1 month 3 Table space of day tools Backup of . stay 2 month 21 Day to day tablespace tools Make a recent backup ,RMAN Let the media manager include 1 month 3 The tape of daily backup is set as expired .

2.2. SBT Redundancy of backup backup optimization of retention policy

Suppose a redundancy retention policy is configured . In this case , When it exists r+1 Backup of files （r Is the command CONFIGURE RETENTION POLICY TO REDUNDANCY r Redundancy in ）,RMAN Only skip backing up offline or read-only data files to SBT.

for example , Assume that backup optimization is enabled and the following retention policies are set ：
CONFIGURE DEFAULT DEVICE TYPE TO sbt;
CONFIGURE BACKUP OPTIMIZATION ON;
CONFIGURE RETENTION POLICY TO REDUNDANCY 2;

Use these configurations ,RMAN Skip backing up only three identical files that have already been backed up . Assume you have never backed up users Table space , It's readable and writable , During the course of a week, perform the actions in the following table .

God	operation	result	Redundant backup
Monday	Normal offline users Table space
Tuesday	BACKUP DATABASE	Backup tablespaces users
Wednesday	BACKUP DATABASE	Backup tablespaces users
Thursday	BACKUP DATABASE	Backup tablespaces users	Tuesday's backup
Friday	BACKUP DATABASE	Table space users No backup	Tuesday's backup
Saturday	BACKUP DATABASE	Table space users No backup	Tuesday's backup
Sunday	DELETE OBSOLETE	Tuesday's backup was deleted
Monday	BACKUP DATABASE	Backup tablespaces users	Wednesday backup

On Tuesday , Wednesday and Thursday backup offline users Table space to satisfy the need to exist 3 Conditions for backup （ More than redundancy settings 1）. Friday and Saturday backups will not back up tablespaces because of backup optimization users. Tuesday's backup is expired from Thursday .

On Sunday , Delete all expired backups , It will remove Tuesday's users Backup of table space . Tuesday's backup expires because of the retention policy settings . The backup of the entire database on Monday will be backed up users Table space to meet 3 Conditions that a backup must exist （ More than redundancy settings 1）. such , Tape can be recycled over time .

3． Configure backup optimization

By default , Backup optimization configuration is OFF. have access to SHOW BACKUP OPTIMIZATION Command to view the current settings for backup optimization .

View the current backup optimization configuration ：
SHOW BACKUP OPTIMIZATION;
RMAN configuration parameters for database with db_unique_name PROD1 are:
CONFIGURE BACKUP OPTIMIZATION OFF;

Enable backup optimization ：
CONFIGURE BACKUP OPTIMIZATION ON;

source ：《Oracle Database Backup and Recovery User’s Guide,19c》