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Unix Backup and Recovery by W. Curtis Preston

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Backing Up an RDBMS

Protecting an RDBMS is very complex. There are several storage elements, including datafiles, rollback logs, transaction logs, and the master database. How you get all of the data to a secondary storage medium if it’s changing all the time?

Physical and Logical Backups

There are two primary methods of backing up an RDBMS: physical backups and logical backups. A physical backup physically backs up the data files. This also is referred to as a database backup. There are also two types of physical backups, a cold backup and a hot backup. A cold backupis done by quiescing, or shutting down, the database prior to doing the backup. This is often the simplest way to do a database backup, especially if your database’s data files reside in the filesystem. All you have to do is shut down the database and run your normal filesystem backup utility. Unfortunately, this method may require your database to be shut down for a long time. That is why more and more environments are performing hot backups, which are done while the database is online. This, of course, requires a lot more work behind the scenes, since you are trying to copy the data files while the database is writing to them. This requires a backup utility that understands the internal structure of the database. The purpose of this utility is to log the changes to a particular datafile while it is being copied to the backup media. This allows for a consistent backup image.

A logical backup copies, or exports ...

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