Question

Difference between Complete and InComplete Recovery ?

Answer 1

Complete Recovery

Complete recovery involves using redo data or incremental backups combined with a backup of a database, tablespace, or datafile to update it to the most current point in time. It is called complete because Oracle applies all of the redo changes contained in the archived and online logs to the backup. Typically, you perform complete media recovery after a media failure damages datafiles or the control file.

You can perform complete recovery on a database, tablespace, or datafile. If you are performing complete recovery on the whole database, then whether you are using RMAN or SQL*Plus you must:

    Mount the database
    Ensure that all datafiles you want to recover are online
    Restore a backup of the whole database or the files you want to recover
    Apply online or archived redo logs, or a combination of the two

If you are performing complete recovery on a tablespace or datafile, then you must:

    Take the tablespace or datafile to be recovered offline if the database is open
    Restore a backup of the datafiles you want to recover
    Apply online or archived redo logs, or a combination of the two

Incomplete Recovery

Incomplete recovery uses a backup to produce a noncurrent version of the database. In other words, you do not apply all of the redo records generated after the most recent backup. You usually perform incomplete recovery of the whole database in the following situations:

    Media failure destroys some or all of the online redo logs.
    A user error causes data loss, for example, a user inadvertently drops a table.
    You cannot perform complete recovery because an archived redo log is missing.
    You lose your current control file and must use a backup control file to open the database.

To perform incomplete media recovery, you must restore all datafiles from backups created prior to the time to which you want to recover and then open the database with the RESETLOGS option when recovery completes. The RESETLOGS operation creates a new incarnation of the database--in other words, a database with a new stream of log sequence numbers starting with log sequence 1.