1.A transaction is first recorded into the transaction log.

2.Changes required in the transaction are then applied to cached pages.

3.From time to time sets of modified pages are flushed to data files on disk.

Filesystem backup of databases and applications

Databases are constantly changing while they are online. Database servers consist of multiple components that minimize response time for connected users and increase performance. Some data is kept in the internal cache memory and some in temporary log files, which are flushed at checkpoints.

Because data in a database can change during a backup, a filesystem backup of database files makes no sense without putting the database server into a special mode or even offline. Saved database files have to be in a consistent state, otherwise the data is of no use.

The following steps are required to configure a filesystem backup of the database or application:

•identify all data files

•prepare two programs that are able to shut down and start up the database, respectively

•configure the filesystem backup specification with all the data files included and specify the shut-down program as a pre-exec command and the start-up program as a post-exec command

This method is relatively simple to understand and configure but has one key disadvantage: the database is not accessible during the backup, which is unacceptable for most business environments.

Online backup of databases and applications

To overcome the necessity to shut down the database during a backup, database vendors have prepared interfaces that can be used to put databases temporarily into special modes to save the data to tapes. Server applications are thus online and available to users during the backup or restore process. These application-specific interfaces allow backup products, like Data Protector, to back up or restore logical units of the database application. The functionality of the backup APIs varies depending on the database vendor. Data Protector integrations are available for major databases and applications. For a detailed list of supported integrations, see the HP Data Protector product announcements, software notes, and references.

Concepts guide

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