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Oracle backup and recovery Interview Questions and answwer-- 5 in oracle

How would you decide your backup strategy and timing for backup?In fact backup strategy is purely depends upon your organization business need.
If no downtime then database must be run on archivelog mode and you have to take frequently or daily backup.
If sufficient downtime is there and loss of data would not affect your business then you can run your database in noarchivelog mode and backup can be taken in-frequently or weekly or monthly.
In most of the case in an organization when no downtime then frequent inconsistent backup needed (daily backup), multiplex online redo log files (multiple copies), different location for redo log files, database must run in archivelog mode and dataguard can be implemented for extra bit of protection.

What is difference between Restoring and Recovery of database?
Restoring means copying the database object from the backup media to the destination where actually it is required where as recovery means to apply the database object copied earlier (roll forward) in order to bring the database into consistent state.

What is the difference between complete and incomplete recovery?An incomplete database recovery is a recovery that it does not reach to the point of failure. The recovery can be either point of time or particular SCN or Particular archive log specially incase of missing archive log or redolog failure where as a complete recovery recovers to the point of failure possibly when having all archive log backup.

What is the benefit of running the DB in archivelog mode over no archivelog mode?
When a database is in no archivelog mode whenever log switch happens there will be a loss of some redoes log information in order to avoid this, redo logs must be archived. This can be achieved by configuring the database in archivelog mode.

If an oracle database is crashed? How would you recover that transaction which is not in backup?If the database is in archivelog we can recover that transaction otherwise we cannot recover that transaction which is not in backup.

What is the difference between HOTBACKUP and RMAN backup?
For hotbackup we have to put database in begin backup mode, then take backup where as RMAN would not put database in begin backup mode. RMAN is faster can perform incremental (changes only) backup, and does not place tablespace in hotbackup mode.

Can we use Same target database as Catalog database?
No, the recovery catalog should not reside in the target database (database to be backed up) because the database can not be recovered in the mounted state.

Incremental backup levels:
Level 0 – full backup that can be used for subsequent incrementals
RMAN> backup incremental level 0 database;
Differential Level 1–only the blocks that have changed since the last backup (whether it is level 0 or level 1)
RMAN> backup incremental level 1 differential database;
Cumulative Level 1 – all changes since the last level 0 incremental backup
RMAN> backup incremental level 1 cumulative database;
A full backup cannot be used for a cumulative level 1 backup.
A cumulative level 1 backup must be done on top of an incremental level 0 backup.

Why RMAN incremental backup fails even though full backup exists?If you have taken the RMAN full backup using the command ‘Backup database’, where as a level 0 backup is physically identical to a full backup. The only difference is that the level 0 backup is recorded as an incremental backup in the RMAN repository so it can be used as the parent for a level 1 backup. Simply the ‘full backup without level 0’ can not be considered as a parent backup from which you can take level 1 backup.

Can we perform RMAN level 1 backup without level 0?If no level 0 is available, then the behavior depends upon the compatibility mode setting (oracle version).
If the compatibility mode less than 10.0.0, RMAN generates a level 0 backup of files contents at the time of backup.
If the compatibility is greater than 10.0.0, RMAN copies all block changes since the file was created, and stores the results as level 1 backup.

How to put Manual/User managed backup in RMAN?In case of recovery catalog, you can put by using catalog command:
RMAN> CATALOG START WITH ‘/oracle/backup.ctl’;

How to check RMAN version in oracle?If you want to check RMAN catalog version then use the below query from SQL*plus
SQL> Select * from rcver;

What happens actually in case of instance Recovery?While Oracle instance fails, Oracle performs an Instance Recovery when the associated database is being re-started. Instance recovery occurs in 2 steps:
Cache recovery: Changes being made to a database are recorded in the database buffer cache as well as redo log files simultaneously. When there are enough data in the database buffer cache, they are written to data files. If an Oracle instance fails before these data are written to data files, Oracle uses online redo log files to recover the lost data when the associated database is re-started. This process is called cache recovery.
Transaction recovery: When a transaction modifies data in a database (the before image of the modified data is stored in an undo segment which is used to restore the original values in case the transaction is rolled back). At the time of an instance failure, the database may have uncommitted transactions. It is possible that changes made by these uncommitted transactions have gotten saved in data files. To maintain read consistency, Oracle rolls back all uncommitted transactions when the associated database is re-started. Oracle uses the undo data stored in undo segments to accomplish this. This process is called transaction recovery.

My Database has Level 1 backup, tell me what are all backed up ? with Example?

Database is UP and has taken Level 0 backup, is the backup taken is Consistent or Inconsistent?

How do you say a backup is Consistent or Inconsistent, Oracle Terminology?

Can we take backup when the Database is down?

If i have a RMAN full backup Level 0 of Sun @9PM, on Mon 9PM taken incremental Level 1 backup.What type of backup do you get and what is actually backedup?

If i have a RMAN full backup of Sun @9PM, on Mon 9PM taken incremental Level 1 backup.On Tuesday Database Crashed.What type of backup do you get and what is actually backedup?

There is no Backup available, Can we take a Level 1 backup?

A table got dropped between 9AM - 11AM how to get the Table backup using RMAN,
DB size 500GB available mount point space for table recovery is 15GB?

Sys Admin has changed the time from 10:00 AM to 9:30 AM, table dropped, How do you recover the Table?

A DATAFILE is corrupted and there is no backup, How to recover the datafile?

All Controlfiles are corrupted, How to recover the controlfile?


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