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Tushar Kathe

We are presently having 100GB of DB. We are taking level 0 or complete backup every Sunday and differential incremental level 1 every day.

We want to change it to level 0 or complete backup once in a month (some time mid of month). Cummulative backup every Sunday and incremental rest of the week days. What issues can we face in terms of recovery time if we go about with it?

you will have a long recovery time if you want to do it the day before the next backup - plus you need the space to hold a months worth of backups
Hi Tusher,

We have a 300GB database that we backup daily with RMAN (10g RAC). By using 2 channels and compressed backupset, the entire process takes about 4 hours (backup and backup verification) and only takes 30GB space.

From a recovery perspective, I try to stay away from incremental backups as this increases the recovery time.

Al our databases are 24/7/365 OLTP, DW, or hybrids and we have never had any severe performance impact due to RMAN running the backup.

The strategy you are suggesting would affect your recovery severely.

May I ask why you want to change your current strategy?
The MTTR (mean time to recovery) is the max time required to restore the full backup + applying the incrementals.

For the time to apply incrementals, this depends on the parallelism.

Have you considered enabling parallel recovery?

Parallel Recovery

Recovery performed in parallel can speed up the crash, instance, and media recovery considerably. During a parallel recovery process, the SMON background process reads the redo-log files sequentially, and the redo-blocks are then distributed evenly to all recovery processes to be read into the buffer cache. The parallel slave processes apply the changes to data files. If the data files involved in the recovery are many, the parallel process really helps.

To specify the number of concurrent recovery processes for instance or crash recover use the recovery_parallelism initialization parameter to specifies the number of concurrent recovery processes. This parameter has no affect on media recovery. To parallelize media recovery, use the parallel clause in the RECOVER DATABASE statement.

The SQL*Plus recovery_parallelism command specifies parallel media recovery. The default is NOPARALLEL.



For media recovery, Oracle uses a division of labor approach to allocate different processes to different data blocks while rolling forward, thereby making the procedure more efficient. For example, if parallel recovery is performed with parallel four, and only one data file is recovered, four spawned processes read blocks from the data file and apply records instead of only one process.

Recovery with Oracle Database 10g RAC is automatically parallel for these three stages of recovery:

* Restoration of data files.

* Application of incremental backups.

* Application of redo logs.

The number of channels configured for a RAC database in RMAN determines the degree of parallelism for data file restoration. In the previous example configuration, two streams could have been involved in restoring data files since two channels were configured. The degree of parallelism for restoration of incremental backups is also dependent on the number of configured channels.

Redo logs are applied by RMAN using the degree of parallelism specified in the initialization parameter recovery_parallelism.

In Oracle Database 10g, there is no server manager program, so all DBA functions are done through SQL*PLUS. Using manual recovery methods such as SQL*PLUS, values can be specified for recovery_parallelism, since it is a dynamic parameter. However, it cannot exceed the setting for parallel_max_servers. Using the DEGREE option for the RECOVER command, the degree of parallelism can also be controlled for other recovery operations.
Thanks for pointing out about the parallelism for recovery HAL9000, never knew about it but definitely going to use it in the future!
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