Saturday 16 April 2016

Difference between Recovery Window & Backup Window

Recovery Window :
A recovery window is a period of time that begins with the current time and extends backward in time to the point of recoverability. The point of recoverability is the earliest time for a hypothetical point-in-time recovery, that is, the earliest point to which you can recover following a media failure.
To configure a retention policy based on recovery window, use

 CONFIGURE RETENTION POLICY TO RECOVERY WINDOW no DAYS;  


 Backup Window : 
A backup window is a period of time during which a backup activity must complete. The BACKUP command supports a DURATION argument which lets you specify how long a given backup job is allowed to run. If you run BACKUP DURATION 4:00 TABLESPACE users; command then the backup of tablespace users will run for 4 hours.

RMAN backs up the specified data at the maximum possible speed. If the backup is not complete in four hours, the backup is interrupted. Any completed backupsets are retained and can be used in restore operations, even if the entire backup is not complete. Any incomplete backupsets are discarded.

By default, when BACKUP … DURATION command runs out of time before the backup completes, RMAN reports an error (The effect of this is that if the command is running in a RUN block, the RUN block terminates.). You can control this behavior by adding the PARTIAL option to the BACKUP … DURATION command, as “BACKUP DURATION 4:00 PARTIAL TABLESPACE users FILESPERSET 1;”.When PARTIAL is used, no error is reported when a backup command is interrupted due to the end of the backup window. Instead, a message showing which files could not be backed will be displayed. If the BACKUP command is part of a RUN block, then the remaining commands in the RUN block will continue to execute.

When using DURATION you can run the backup with the maximum possible performance, or run as slowly as possible while still finishing within the allotted time, to minimize the performance impact of backup tasks. To maximize performance, use the MINIMIZE TIME option with DURATION, as BACKUP DURATION 4:00 PARTIAL MINIMIZE TIME DATABASE FILESPERSET 1; in this command. To extend the backup to use the full time available, use the MINIMIZE LOAD option as BACKUP DURATION 4:00 PARTIAL MINIMIZE LOAD DATABASE FILESPERSET 1;. 

RMAN monitors the progress of the running backup, and periodically estimates how long the backup will take to complete at its present rate. If RMAN estimates that the backup will finish before the end of the backup window, it slows down the rate of backup so that the full available duration will be used. This reduces the overhead on the database associated with the backup 

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