Most Common Questions

1 How do you verify and validate the Datafile which is backed up?
Answers

In rman list recoverable backup of database

Use RMAN Backup validate database.

It will performs a validation of the datafiles by checking for logical and physical block corruption.

No backupsets are created.

To verify that the datafile is particularly backed up or not.

Sql>select * from v$backup-->This will shows the status of a particular file.
sql>select * from v$recover_file-->This is show whether any file has to be recovered.

use dbverify to validate the backups.thanks

The DBVERIFY Utility

An OS executable (dbv in $ORACLE_HOME/bin) used to verify datafiles

Works against datafiles live or backup But doesnot work on Backup sets...

Works for datafiles on raw devices but you must give it a range of blocks to look at.

In the output it refers to blocks as pages . Block 5 would be page 5.

RMAN performs its own validation when backing up so dbv is not necessary. It can be used on user backups (aka non-RMAN backups).

If a block is influx then DBV was forced to check it multiple times because it was in use.

2 How much time will it take a hotbackup if the batabase size is 60Gb?

Answers

 It depends on the datafiles related to database at OS Level.

Depends upon number of servers and RAM.

Depends on the amount of data inside the database.

Its all upto the Kind of Server and No of server Parameters configured and the type of backup device

Depends! On the I/O at that time...

Hot backup involves many Steps including - taking the particular Tablespace in begin backup mode and then copying the file to Backup directory.

It all depends on the Server Configuration & I/O at that time. Generally the DB will be stored on EMC - where EMC connects to large number of Servers.

3. What is mean live dead lock? How to prevent it.?

Answers

When there r 2 or more process run at a time and want to same resource then if one process take resource and othere process want same resource then there will be dedlock occour.

A deadlock occurs when two or more users are waiting for data locked by each other(Not commited by user01).

To fix this recreate the segment with higher INITTRANS and/or PCTFREE values. This will allow more space in the data blocks for Oracle to allocate more transaction entries (24 bytes at a time) when required

4. What is the difference between recovery and restoring of the database?

Answers

Restoring a database is copying the physical files from a backup medium (disk or tape) to the appropriate file locations for database operation

Recovery is process of updating database files restored from backup w/changes made to the database since backup, typically using redo log files.(Restored backup files + changes = Recovery)

5. What are the different tools available for hot backups?

Answers

Hot backup can be done by either RMAN,User Managed Backups by puting tablespace in backup mode my OEM which does the same as the user managed backup.But the Backup depends upon the size of the database you are using . if the database size in TB the RMAN backup will take more than 10 hours to complete and if the database is critical you can' wait for long to go for so long in this case their are special backup techniques which are given by vendors like TIVOLI and Netbackup they provide BC Vol backup called Business content Volumn Sync which copies a snapshot of the primary data to another place and backsup the database from one SAN to another with in 15 min for 2 TB of database and is the preferable method for big companies.

6 How can I Export 9i data in 8i ? I mean when I Export from 9i and Import in 8i, I face errors. what sould i do?
Answers

Follow these steps
1) Install Oracle 8i Client
2) Export database from Oracle 8i Client PC
3) Import data into Oracle 8i Database.

execute catexp.sql of 8 in oracle 9i then take export and then import in 8 database.

7. what is the difference between media recovery and crash recovery..?

Answers

Media recovery is a process to recover database from backup when physical disk failure occure.
Cash recovery is a automated process take care by oracle when instance failure occure.

8. what do you mean by MEDIA RECOVERY..?

Answers

Loss of tablespaces, datafiles, controlfile, tables it is media failure and we need to recover such a tablespaces, datafiles, controlfile or tablespace through latest backup
It is MEDIA recovery.

9. what is the disk migration?what isthe steps involved in diskmigration?

Answers

Disk migration is noting but migration of data from one OS dependent database to another Dependent database. The steps involved in this are

- first go to your target database and export all your data into flat files

-next in the destination database during the installation of the database it asks for data source instead of giving the data of the oracle provided give the path of the flat file you exported previously .

10. What are the steps involved in Database Startup ?

Answers

Start Instance, Mount database and open for user access
Step1 :: Read parameter file and verify parameters(Memory Initialization & Background Process started)
Step 2 :: Mount the database and Read the control file information but No verification against this data will be done at this stage.
Step 3:: Open database and before opening verify Control file Contents and synchronize Redo files and data files with the respect to Transactions and then open the database.

11. What are the steps involved in Database Shutdown?

Answers

Close the Database, Dismount the Database and Shutdown the

Instance.

Different types of Shutdown

There are four types of shutdown

Shutdown Normal - Normal is the default mode, here new user can't logon to the database, but the current user can start the new transaction and work till he wants, the database shutdown only after the last user logs off.

Shutdown Transactional - here new user can't logon to the database, and the current user can't start the new transaction, once the current transaction complets, database shutdown.

Shutdown Immediate - here new user can't logon to the database, user can't start the new transaction, the current transactions rolls back, and database shutdown.

Shutdown Abort - here new user can't logon to the database, user can't start new transaction, the current transaction is not rolled back, database shutdown's.

While shutting down oracle updates data file header and control file with the current checkpoint informanation, Except Shutdown Abort the checkpoint is same in datafile header and control file it means database is consistance and it is clean shutdown. If the checkpoint is not same at both locations then instance recovery required at next startup.

12. What is Restricted Mode of Instance Startup ?

Answers

By starting Instance in restricted mode it will not allow all users to access and only users with restriction privilege will be allowed to access.
This will be done time of make some data changes so that no users should be allowed to access data on time of changes happening

To Enable Restricted Session
Alter system enable restricted session;

To Disable Restricted Session
Alter system disable restricted session;

To Start the Database in Restricted Mode
STARTUP RESTRICT

13. What are the different modes of mounting a Database with the Parallel Server ?

Answers

Exclusive  Mode  If  the  first  instance that mounts a

database does so in exclusive mode, only that Instance can

mount the database.

Parallel  Mode   If the first instance that mounts a

database is started in parallel  mode,  other instances that

are started in parallel mode can also mount the database.

14. What is Full Backup ?
Answers

A full backup is an operating system backup of all data files, on-line redo log files and control file that constitute ORACLE database and the parameter.

15. Can Full Backup be performed when the database is open ?

 Answers

Yes we can perform the database backup when database is up and running. We can make it by using user managed backups and RMAN backups.

use we can take full backup while database is open. By using hot backup. Take backup of all tablespaces using hotback and take backup on control file using alter database backup controlfile to trace; and then take backup of pfile using: create pfile from spfile; In this way Full backup can be performed when the database is open;

16. What is Partial Backup ?

Answers

A Partial Backup is any operating system backup short of a full backup, taken while the database is open or shut down.

17. What is On-line Redo Log?

18. What is Mirrored on-line Redo Log ?

Answers

A mirrored on-line redo log consists of copies of on-line redo log files physically located on separate disks, changes made to one member of the group are made to all members.

19. What is Archived Redo Log ?

Answers

Archived Redo Log is defined as a copy of one of the filled members of an online redo log group. It is maintained when the database is in the ARCHIVELOG mode

20. What are the advantages of operating a database in ARCHIVELOG mode over operating it?

Answers

If you run in NOARCHIVELOG mode, if your database crashes, you can only recover to the point of time of your last backup.

ARCHIVELOGMODE allows you to recover to the point of the crash. Downside is it takes more diskspace and can cause the db to freeze if that disk fills up. If you have a production system with no tolerance for loss, this isn't an option.

21. What are the steps involved in Instance Recovery ?

Answers

Rolling  forward to recover data that has not been recorded

in data files, yet  has  been recorded  in the on-line redo

log, including the contents of rollback segments.

Rolling back transactions that have been explicitly rolled

back or have not been committed as indicated by the rollback

segments regenerated in step a. 

Releasing any resources (locks) held by transactions in

process at the time of the failure.

Resolving  any  pending  distributed  transactions 

undergoing  a two-phase commit at the time of the instance

failure.