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This article introduces the relevant knowledge of "what are the relevant concepts of database backup". In the operation of actual cases, many people will encounter such a dilemma. Next, let the editor lead you to learn how to deal with these situations. I hope you can read it carefully and be able to achieve something!

Type of backup

There are two types of backups: physical backup and logical backup.

(1) physical backup (Physical Backups)

The core of physical backup is to copy files and copy them to other paths or storage devices. For oracle, it mainly copies data files, control files, archive files, parameter files, password files and so on.

To achieve physical backup: mainly RMAN (Recovery Manager).

(2) logical backup (Logical Backups)

The core of logical backup is to copy data, which does not care where the data is stored or in which file, but only uses command tools to export and save the data.

Logical backup implementation: exp, expdp and dblink+create table as and so on.

The status of the database at the time of backup

According to the status of the database at the time of backup, it can be divided into cold backup and hot backup.

(1) Hot backup (Online Backups)

A hot backup is a backup created in the startup state of a database, also called an online backup. The backup created under the hot backup must be an inconsistent backup. We will talk about the concept of inconsistent backup in a moment. If you want to create a valid hot backup, the database must be in an archived state, because only by using archived logs or online redo log files can the database be restored to a consistent state.

(2) Cold backup (Offline Backups)

A cold backup is a backup that occurs when the database is closed, also known as offline backup. Cold backup is not necessarily a consistent backup. If the database is normally closed or the database is open read only, to put it simply, when the database does not write data normally, such a backup is a cold backup of a consistent backup. A consistent backup can directly repair (restore) the database without the recover operation, the so-called restore operation. Is to use archiving or redo log to restore data to a consistent state, and for such a backup state, even if archiving is not opened, it does not affect the data recovery operation at all. If the database is shut down abnormally, such as shutdown abort or power outage and shutdown of the host, the cold backup is an inconsistent backup. If archiving is enabled, it can also be restored using archived logs and online redo log files. If archiving is not enabled, such an inconsistent backup will be an invalid backup.

III. Status of backup

It can be divided into two categories: consistent and inconsistent.

(1) consistent backup (Consistent Backups)

Data files and control files for consistent backups have the same SCN (System Change Number). A backup created is a consistent backup only if the database is closed in shutdown [normal | immediate | transactional] and the database is not left open (or open read only). This backup can be opened without a restore operation after repair.

(2) inconsistent backup (Inconsistent Backups)

A backup created when a database is in an inconsistent state is an inconsistent backup, which is usually an inconsistent backup when a database is open read write or shutdown abort.

Third, divide according to the size of the backup

It can be divided into:

Full backup (whole database backups)

Tablespace backup (tablespace backups actually backs up data files)

Data file backup (datafile buckups)

Control file backup (control backups)

Backup of archived log files (archived redolog backups)

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