Sunday 8 February 2015

Latest Oracle Database Interview Questions and Answers (Page 4)

Below are some important Oracle Database interview questions which are asked in most MNC company interviews for beginners or professionals.

31. How Much Memory Your 10g XE Server Is Using?
Your 10g XE Server is using about 180MB of memory even there is no users on the server. The server memory usage is displayed on your server home page, if you log in as SYSTEM.

32. How To Start Your 10g XE Server from Command Line?
You can start your 10g XE server from command line by:
* Open a command line window.
* Change directory to oraclexeapporacleproduct10.2.0serverBIN.
* Run StartDB.bat.
The batch file StartDB.bat contains:
net start OracleXETNSListener
net start OracleServiceXE
@oradim -startup -sid XE -starttype inst > nul 2>&1

33. How To Shutdown Your 10g XE Server from Command Line?
You can shutdown your 10g XE server from command line by:
* Open a command line window.
* Change directory to oraclexeapporacleproduct10.2.0serverBIN.
* Run StopDB.bat.
The batch file StopDB.bat contains:
net stop OracleServiceXE

34. How To Unlock the Sample User Account in Oracle?
Your 10g XE server comes with a sample database user account called HR. But this account is locked. You must unlock it before you can use it:
* Log into the server home page as SYSTEM.
* Click the Administration icon, and then click Database Users.
* Click the HR schema icon to display the user information for HR.
* Enter a new password (hr) for HR, and change the status to Unlocked.
* Click Alter User to save the changes.
Now user account HR is ready to use.

35. How To Change System Global Area (SGA) in Oracle?
Your 10g XE server has a default setting for System Global Area (SGA) of 140MB. The SGA size can be changed to a new value depending on how many concurrent sessions connecting to your server. If you are running this server just for yourself to improve your DBA skill, you should change the SGA size to 32MB by:
* Log into the server home page as SYSTEM.
* Go to Administration, then Memory.
* Click Configure SGA.
* Enter the new memory size: 32
* Click Apply Changes to save the changes.
* Re-start your server.

36. How To Change Program Global Area (PGA) in Oracle?
Your 10g XE server has a default setting for Program Global Area (PGA) of 40MB. The PGA size can be changed to a new value depending on how much data a single session should be allocated. If you think your session will be short with a small amount of data, you should change the PGA size to 16MB by:
* Log into the server home page as SYSTEM.
* Go to Administration, then Memory.
* Click Configure PGA.
* Enter the new memory size: 16
* Click Apply Changes to save the changes.
* Re-start your server.

37. What Happens If You Set the SGA Too Low in Oracle?
Let's you made a mistake and changed to SGA to 16MB from the SYSTEM admin home page. When you run the batch file StartDB.bat, it will return a message saying server stated. However, if you try to connect to your server home page: http://localhost:8080/apex/, you will get no response. Why? Your server is running, but the default instance XE was not started.
If you go the Control Panel and Services, you will see service OracleServiceXE is listed not in the running status.

38. What To Do If the StartBD.bat Failed to Start the XE Instance?
If StartBD.bat failed to start the XE instance, you need to try to start the instance with other approaches to get detail error messages on why the instance can not be started.
One good approach to start the default instance is to use SQL*Plus. Here is how to use SQL*Plus to start the default instance in a command window:
>cd (OracleXE home directory)
>.binstartdb
>.binsqlplus
Enter user-name: SYSTEM
Enter password: atoztarget
ERROR:
ORA-01034: ORACLE not available
ORA-27101: shared memory realm does not exist
The first "cd" is to move the current directory the 10g XE home directory. The second command ".binstartdb" is to make sure the TNS listener is running. The third command ".binsqlplus" launches SQL*Plus. The error message "ORA-27101" tells you that there is a memory problem with the default instance.
So you can not use the normal login process to the server without a good instance. See other tips on how to log into a server without any instance.

39. How To Login to the Server without an Instance?
If your default instance is in trouble, and you can not use the normal login process to reach the server, you can use a special login to log into the server without any instance. Here is how to use SQL*Plus to log in as as a system BDA:
>cd (OracleXE home directory)
>.binstartdb
>.binsqlplus
Enter user-name: SYSTEM/atoztarget AS SYSDBA
Connected to an idle instance
SQL> show instance
instance "local"
The trick is to put user name, password and login options in a single string as the user name. "AS SYSDBA" tells the server to not start any instance, and connect the session the idle instance.
Log in as SYSDBA is very useful for performing DBA tasks.

40. How To Use "startup" Command to Start Default Instance?
If you logged in to the server as a SYSDBA, you start the default instance with the "startup" command. Here is how to start the default instance in SQL*Plus in SYSDBA mode:
>.binsqlplus
Enter user-name: SYSTEM/atoztarget AS SYSDBA
Connected to an idle instance
SQL> show instance
instance "local"
SQL> startup
ORA-00821: Specified value of sga_target 16M is too small,
needs to be at least 20M
Now the server is telling you more details about the memory problem on your default instance: your SGA setting of 16MB is too small. It must be increased to at least 20MB.
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