Databases Reference
In-Depth Information
During a recovery, RMAN will automatically determine how to apply redo. First, RMAN will apply any
incremental backups available that are greater than level 0, such as the incremental level 1. Next, any archived redo
log files on disk will be applied. If the archived redo log files do not exist on disk, then RMAN will attempt to retrieve
them from a backup set.
■
an rman incremental backup contains copies of only those database blocks that have changed from the
previous incremental backup. rman can more efficiently recover a data file using an incremental backup over applying
redo from an archived redo log file.
Note
This chapter guides you through several different common (and not so common) restore and recovery scenarios.
Now that you understand the mechanics, you are much better prepared to determine which steps you should take to
restore and recover your database.
Determining How to Restore and Recover
Problem
You just experienced a media failure, and you're not sure what commands you'll need to run to restore and recover
your database.
Solution
To be able to perform a complete recovery, all of the following conditions need to be true:
•
Your database is in archivelog mode.
•
You have a good baseline backup of your database.
•
You have any required redo that has been generated since the backup (archived redo log
files, online redo log files, or incremental backups that RMAN can use for recovery instead of
applying redo).
There are a wide variety of restore and recovery scenarios. How you restore and recover depends directly on
your backup strategy and what files have been damaged. Listed next are the general steps to follow when facing
a media failure:
1.
Determine what files need to be restored.
2.
Depending on the damage, set your database mode to nomount, mount, or open.
3.
Use the
restore
command to retrieve files from RMAN backups.
4.
Use the
recover
command for data files requiring recovery.
5.
Open your database.
Your particular restore and recovery scenario may not require that all of the previous steps be performed.
For example, you may just want to restore your spfile, which doesn't require a recovery step.
