Interview Questions - Oracle Backup and Recovery

The following quesitons are from: http://www.geekinterview.com/Interview-Questions/Oracle/Backup-and-Recovery


1. What is the differenec between recovery and restoring of the database?

ans:
- Restoring a database is the replacement of lost or damaged file with a backup.
- You can retore files either with operating system commands as UNIX cp or the RMAN RESTORE COMMAND.
- Recovering a database is the appliaciton of redo data or incremental backups to database files in order to reconstuct lost changes.
- The three types of recovery are instance recovery, crash recovery and media recovery.
- Oracle performs the first two types of recovery automatically using online redo records; only media recovery requres you to restore a backup and issue commands. Only Recovery Manager can recover datafiles by applying incremental backups.

2. What are the different tools are available for hot backup? Is it perferable to take it manually all the time or it depends on the size of the database?
ans:
- hot backup(online backup): A backup of one or more datafiles taken while a database is open and the datafiles are online
- user-managed backup while the database is open: first must put the tablespace in backup mode by issing an ALTER TABLESPACE BEGIN BACKUP command
- RMAN backup: do not need to put the tablespace in backup mode
- OEM
- (cited): if the databse size in TB the RMAN backup will take more than 10 hours to complete
- special backup techiniques which are given by vendors like TIVOLI and Netbackup:
Business content Volume Sync which copies a snapshot of the primiary data to another palce and backup the database from one SAN to another within 15 min for 2TB of database and is the preferable method for big company


3. What is the difference between media recovery and crash recovery

Ans: Media recovery is the applicaiton of redo or incremental backups to a restored backup datafile or individual data block to bring it to a specified time.
- Datafile media recovery always begins at the lowest SCN recorded in the datafile headers.
- when perform media recovery, you an recover:
* The whole database
* A tablespace
* A datafile
* A set of blocks whithin a datafile
- Typically, you perform media recovery after a media failure damages some or all of the database files
crash recovery is the automatic application of oneline redo records to a database after either a single-instance database crashes or all instances of an Oracle Real Application Cluster configuration crash. Crash recovery only requires redo from the online logs: archive redo logs are not required


4. What are the steps involved in Database startup?
Ans: steps are:
Nomount stage (start an instance)
- read initialization parameter file
- SGA is allocated
- background process are started
- alert log file is opened

Mount stage
- control files is read
- name & location of the datafiles, logfiles are detected

Open stage
- opens the online datafiles and online redo log files.
- note: If a tablesace was offline when the database was previously shut down, the tablespace and its corrensponding datafiles will still be offline when you reopen the database.

5. What are steps involved in database shutdown?
ans:
(1) Close the database
- Oracle writes all database data and recovery data in the SGA to the datafiles and redo log files, respectively.
- Next, Oracle closes all online datafiles and online redo log files.
(2) Unmount the database
- After the database is closed, Oracle unmounts the database to disassociate it from the instance. - At this point, the instance remains in the memory of your computer.
- After a database is unmounted, Oracle closes the control files of the database.
(3) Shutdown the instance
- SGA is removed from memory and the background processes are terminated.