RMAN backup database_ Manage backup window

This section describes how to use the backup window to set limits on the time span that a backup job can complete .

1． About the backup window

The backup window is a time period , During this time period, the backup must be completed . for example , You may want to restrict database backups to a time window when user activity on the system is low , such as 2:00am and 6:00am Between .

RMAN First, back up the least recently backed up files . By default ,RMAN Back up files as quickly as possible . Specifying a window does not mean RMAN Backup data faster than normal to ensure that the backup is completed before the end of the window .

By default , If the backup is not in DURATION Within time , that RMAN Interrupt backup and report an error . If BACKUP The command is in a RUN In command , that RUN Order to terminate . Any completed backup set is preserved and can be used in the restore operation , Even if the entire backup is not complete . therefore , If you try an assignment , It is interrupted when the available duration expires , Each succeeding attempt will include （cover） More files to back up . Any incomplete backup sets are discarded .

2． Specify the backup duration （Backup Duration）

Use BACKUP Ordered DURATION Parameter specifies how long a hypothetical backup job is allowed to run .

Specify a backup duration ：
1） start-up RMAN, Connect to the target database and recovery Directory （ If used ）.
2） perform BACKUP DURATION command .
for example , stay 2:00 a.m Run the command , Specify that the backup run until 6:00 a.m：

BACKUP
 DURATION 4:00
 TABLESPACE users;

3． Allow partial backups in the backup window （Partial Backup）

When specifying PARTIAL, When the backup is interrupted due to the end of the backup window ,RMAN An error will not be reported . contrary ,RMAN Displays a message listing which files were not backed up .

If BACKUP yes RUN Part of a block , that RUN The remaining commands in the block continue .

If specified FILESPERSET 1, that RMAN Place each file in its own backup set . When the backup is interrupted at the end of the backup window , Only the backup of the file currently being backed up will be lost . All backup sets completed during the window are saved , Minimize the loss of work caused by the end of the backup window .

Block when backup is partially complete RMAN Make a mistake ：
1） start-up RMAN, Connect to the target database and recovery Directory （ If used ）.
2） perform BACKUP DURATION Command and PARTIAL Options .
for example , stay 2:00 a.m Run the command , Specify that the backup run until 6:00 a.m And each data file in a different backup set ：
BACKUP
 DURATION 4:00 PARTIAL
 TABLESPACE users
 FILESPERSET 1;

4． Minimize backup load and duration

When using DURATION when , You can run backups with the highest possible performance , Or run as slowly as possible to minimize the performance impact of the backup task when it can still be completed within the allotted time .

To maximize performance , and DURATION Use it together MINIMIZE TIME Options , As shown below ：
BACKUP
 DURATION 4:00 PARTIAL
 MINIMIZE TIME
 DATABASE
 FILESPERSET 1;

In order to extend the backup time, use the partially available time , Use MINIMIZE LOAD Options , As shown below ：
BACKUP
 DURATION 4:00
 MINIMIZE LOAD
 DATABASE
 FILESPERSET 1;

In this example ,RMAN Monitor the progress of running backups , Periodically estimate how long backups will take to complete at the current rate . If RMAN It is estimated that the backup will be completed before the backup window , So it slows down the backup , So all available durations are used . This will reduce the consumption associated with backup on the database .

When used in tape backup DURATION and MINIMIZE LOAD when , Note the following ：
1） Effective backup to tape requires tape streaming （streaming）. If you use MINIMIZE LOAD, that RMAN It is possible to reduce the speed of backup to the point where tape streaming is not optimal .
2） RMAN Occupy tape resources for the entire duration of the backup window . This prevents any other purpose from using these tape resources during the backup window .

Because of these factors , It is not recommended to use... When backing up to tape MINIMIZE LOAD.

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