Physical and Logical Backups
- Copy of Datafile using an OS utility such as cp command.
- You can use this file to restore the database contents if you lose the disk file.
- Copy of the files like Datafiles, control files and redo log files.
- logical backups by using Oracle Data pump Export tool wherein you copy the definitions and contents all of the database’s logical componets such as table and so on.
- Its not complete backup and recovery solution.
Whole and Partial backups
- Backup of the entire database.
- Partial backup –> backup of a tablespace or datafile in a database.
- Datafile backup —> only a single OS file.
- Tablespace backup –> all the datafiles that are part of the tablespace.
Online and Offline Backups
- RMAN support both online ( HOT ) and offline ( COLD ) backups.
- An online backup is always inconsistent during a recovery , the application of the necessary archived log file will make the backup consistent.
Full and Incremental Backups
- It will contain complete backups of all the datafiles.
- It contain only the changed data blocks in the datafiles.
- You can make incremental backups only with the help of RMAN.
Consistent and Inconsistent Backups
What is SCN?
- SCN is an Oracle assigned number that indicates a committed version of a database.
- Its quite possible that different datafiles in the database might have a different SCN at any given point in time.
- If the SCN across all the datafiles are synchronized, it means that the data across the datafiles comes from a single point of time and thus, is consistent.
- During each checkpoint, the server makes all the datafiles SCN consistent w.r.t an identical SCN.
- It updates control file with that SCN information.
- This synchronization of the SCN gives you a consistent backup of your database.
- If you backup your database while it’s running, you may end up with backups of the various data files at various time points and different SCN.
- This means your database are inconsistent, since the SCN aren’t identical across all the datafiles.
- If you’re using inconsistent backups, you must use the archive redo log files to make the data current and synchronize the SCN across the datafiles.
- If you’re using the RMAN offline backup, the database must be mounted before you can actually perform the RMAN backup. RMAN needs to update the target database control file.