Oracle backup

What is archive log mode?

The archiving of the redo log is enabled by running database in ARCHIVELOG mode.

A group of filled redo log files cannot be reused by LGWR until the group is archived and become available for archiving immediately after a redo log switch occurs.

Advantages of archiving the filled groups:

• A database backup, together with online and archived redo log files, guarantees recovery of all committed transactions in the event of an operating system or disk failure.
• In an archived log, the backup is taken while the database is open and in normal system use.
• The standby database can be kept current with its original database by continuously applying the original archived redo logs to the standby.

Explain cold and hot backups.

A backup taken when the database is not running is called a cold backup.
This is also known as an offline backup.

Copying physical files when the database is up is called hot back up.
It is done by putting the tablespace in backup mode and then copying all the data file using the copy commands and then bringing it back to normal state.

What are incremental backups?

Incremental backup stores all files that have changed since the last FULL, DIFFERENTIAL OR INCREMENTAL backup.

Its advantage is that it takes very less time to complete.
But the restore operation is lengthy as each incremental backup must be processed.

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