|Lesson 2||Listing methods for minimizing downtime |
|Objective||Identify methods to minimize downtime |
List Methods for Minimizing Downtime
What would you do if there was a media failure and you found out that several
database files were damaged? As an experienced DBA, you know that you must act quickly to keep the database downtime to a minimum. Before you start media recovery, you must determine the nature of the damaged database files and the tablespaces that they belong to. Then you need to choose an appropriate recovery method based on whether the damaged database files are essential or non-essential. Generally speaking, there are three methods that you may incorporate into your recovery strategy to minimize database downtime:
- Start the database with missing datafiles
- Apply parallel recovery to the damaged database files
- Avoid the need for recoveries by multiplexing the online redo logs and control files
Start the database with missing datafiles
If the damaged files are neither control files, nor do they belong to the system or rollback segment tablespaces, you can start the database without them. In this way, you make the database accessible to users who do not need these datafiles. After the database is open, you can recover the damaged datafiles and put them back online when recovery is complete.
Parallel recovery is a very effective way to minimize recovery time. This process allows several datafiles located on different disks to be recovered at the same time. It is especially useful when you have to perform a closed database recovery. For example, if a most of the datafiles are damaged, or if the damaged datafiles belong to the system or rollback segment tablespaces, you can perform parallel recovery.
Multiplexing Control Files and redo logs
The most efficient way to minimize database downtime for recovery is to avoid the need to perform one. If the damaged or lost files are online redo logs or control files, and you have multiplexed these files in your database configuration, you do not need a recovery at all. You simply copy the mirrored files back to their original location and make the database available immediately.
In order to minimize database downtime for the purpose of recovery, all you need to do is to establish a good strategy for your database configuration and recovery process. If you spread the database files onto different disks, or multiplex the online redo logs and the control files, you'll be better prepared in the event of a media failure. The next lesson demonstrates how to start a database with missing datafiles.