Let us we discuss about backup and recovery
what is backup and recovery?
- Backup and recovery is to protect the database against data loss and reconstruct the database after data loss.
- Backup has been splitted into two methods
-Physical backup is a backup of the physical files used in storing and recovering your database.
-Such as datafiles,control files,archived redo log files
-Logical backup is exporting the logical data(table,tablespace,schemas) from a database with an Oracle export utility and stored in a binary file.
-Later we can importing those files to the database corresponding oracle utility
Types of failures
*User error failure
*User process failure (PMON)
*Instance failure (SMON)
*Network failure (Network admin)
- When a program attempts to enter invalid data into an Oracle Table.
- Proper privileges to perform a task.
II)User error failure
- Abnormal disconnect or performing a terminal program error and losing the session connection.
- BG process rollback the uncommitted transaction changes to the data and releases the locks.
- Our Database will be shut down due to Hardware , a power failure and an emergency shutdown procedure.
- Check Alert log and trace files. - Just restarting the Database instance using by STARTUP Command.
- Oracle will do an automatic instance or crash recovery at this point.
- Once we restart the db rolls back the uncommitted transactions from undo segments and rolls forward to committed changes it in the online redo logs
- Net listener, NIC and network connection has failed.
- DBA must configure the multiple network cards.
( Note: in above failures can be solved once we restart the instance)
- User deleting data from table and dropping a table you can use FLASHBACK feature -If the transactions not completed yet, rollback statement.
- Oracle LOGMINER also comes on handy situation like this.
- A media failure is a physical problem with a disk that causes a failure of a read from or write to a disk file that is required to run the database. Any database file can be vulnerable to a media failure. The appropriate recovery technique following a media failure depends on the files affected and the types of backup available.
-Examples of media failure
i) Head crash
II) File corruption
III)Overwriting or deleting of a datafile.
-Any one of the multiplexed control files are deleted or lost because of disk failure you must restore the missing control file from an existing control file.
-Datafiles, undo table space is deleted or lost because of a disk failure.If you lose one of these files, the instance may shutdown or may not shutdown in such case
sql> shutdown abort; Then sql>startup mount
-Restore the datafiles and recover it.
-An entire redo log group lost. if you have atleast one member of the redo log group , your database instance can continue to operating normally.
-Restore the log file by copying one of the other members of the same group.
(source of image:https://docs.oracle.com/cd/E11882_01/backup.112/e10642/rcmintro.htm#BRADV99998)
In above failures can be solved by RMAN and UMAN method that work flow has been given that it