Top 61 Oracle DBA Real Time Questions:

1) How can you see the Current SCN number in the database?
  Select current_scn from v$database;

2) How can you see the Current log sequence number the logwriter is writing in to?
Select * from v$log;

3) If you are given a database, how will you know how many datafiles each tablespace contain?
Select distinct tablespace_name,file_name from dba_data_files;

4). How will you know which temporary tablepsace is allocated to which user?
Select temporary_tablespace from dba_users where username=’SCOTT’;

5) If you are given a database, how will you know whether it is locally managed or dictionary managed?
Select extent_management from dba_tablespaces where tablespace_name=’USERS’;
6) How will you list all the tablespaces and their status in a database?
Select tablespace_name,status from dba_tablespaces;

7) How will you find the system-wide 1) default permanent tablespace, 2) default temporary tablespace 3) Database time zone?
 Select property_name,property_value from database_properties where property_name like ‘%DEFAULT%’;

8) How will you find the current users who are using temporary tablespace segments?

9) How will you convert an existing dictionary managed permanent tablespace to temporary tablespace?
 Not possible

10) Is media recovery required if a tablespace is taken offline immediate?
Not required

11) How will you convert dictionary managed tablespace to locally managed tablespace?
Exec dbms_space_admin.tablespace_migrate_to_local(‘TABLESPACE_NAME’);

12) If you have given command to make a tablespace offline normal, but its not is in transactional read-only mode. How will you find which are the transactions which are preventing the conversion?
 By looking at queries using by those SID (u can get script from net). I suspect the question is not clear.

13) If you drop a tablespace containing 4 datafiles, how many datafiles will be droped at a time by giving a single drop tablespace command?

All datafiles

14) If database is not in OMF, How will you drop all the datafiles of a tablespace without dropping the tablespace itself?
Alter database datafile ‘PATH’ offline drop;

15) How will you convert the locally managed tablespace to dictionary managed?What are the limitations?
 Exec dbms_space_admin.tablespace_migrate_from_local(‘TABLESPACE_NAME’);

SYSTEM tablespace should be dictionary

16) Which parameter defines the max number of datafile in database?
 Db_files and MAXDATAFILES in control file

17) Can a single datafile be allocated to two tablespaces?Why?
 No. because segments cannot space multiple datafiles

18) How will you check if a datafile is Autoextinsible?
Select autoextensible from dba_data_files where file_name=’’;

19) Write command to make all datafiles of a tablespace offline without making the tablspace offline itself?
 Alter database datafile ‘PATH’ offline normal;

20) In 10g, How to allocate more than one temporary tablespace as default temporary tablespace to a single user?
 By using temporary tablespace group

21) What is the relation between db_files and maxdatafiles parameters?
 Both will restrict no of datafiles in the database

22) Is it possible to make tempfiles as read only?

23) What is the common column between dba_tablespaces and dba_datafiles?

24) Write a query to display the names of all dynamic performance views?
Select table_name from dictionary where table_name like ‘v$%’;

25) Name the script that needs to be executed to create the data dictionary views after database creation?

26) Grant to the user SCOTT the RESTRICTED SESSION privilege?
SQL> grant restricted session to scott;
Grant succeeded.

27) How are privileged users being authenticated on the database you are currently working on? Which initialization parameter would give me this information?
 Question not clear .PMON will authenticate at instance level.

28) Which dynamic performance view gives you information about all privileged users who have been granted sysdba or sysoper roles? Query the view?
SQL> desc v$pwfile_users

29) What is the purpose of the DICTIONARY table?
To know data dictionary and dynamic performance view names

30) Write a query to display the file# and the status of all datafiles that are offline?
Select file#,status from v$datafile where status=’OFFLINE’;

31) Write the statement to display the size of the System Global Area (SGA)?
 Show parameter sga
Show sga

32) Obtain the information about the current database? What is its name and creation date?
 Select name,created from v$database;

33) What is the size of the database buffer cache? Which two initialization Parameters are used to determine this value?

Db_cache_size or db_block_buffers

34) What value should the REMOTE_LOGIN_PASSWORDFILE take if you need to set up Operating System authentication?

35) Which initialization parameter holds this value? What does the shared pool comprise of?
 Library cache and data dictionary cache.
Parameter : shared_pool_size

36) Which initialization parameter holds the name of the database?

37) Which dynamic performance view displays information about the active transactions in the database? Which view returns session related information?
 V$transaction, v$session

38) Which dynamic performance view is useful for killing user sessions? Which columns of the view will you require to kill a user session? Write the statement to kill any of the currently active sessions in your database?
V$session (SID, SERAIL#)
Alter system kill session ‘SID,SERIAL#’;

39) What is the difference between the ALTER SYSTEM and ALTER SESSION commands?
 Changes performed using ALTER SYSTEM are either permanent for the memory or database. But for ALTER SESSION, its only for that session

40) Write down the mandatory steps that a DBA would need to perform before the CREATE DATABASE command may be used to create a database?
 Create a pfile or spfile
Create password file
If windows, create instance using ORADIM utility

41) What does the script utlexcpt.sql create? What is this table used for?

It will create EXECEPTIONS table. See below link

42) In which Oracle subdirectory are all the SQL scripts such as catalog.sql/ catproc.sql /utlexcpt.sql etc…? Located?

43) Which dynamic performance view would you use to display the OPTIMAL size of the rollback segment RBS2. Write a query to retrieve the OPTIMAL size and Rollback segment name?
 V$undostat (but many scripts are available on Google or even on my blog)
44) During a long-running transaction, you receive an error message indicating you have insufficient space in rollback segment RO4. Which storage parameter would you modify to solve this problem?
 Extent size

45) How would I start the database if only users with the RESTRICTED SESSION privilege need to access it?
 Startup restrict

46) Which data dictionary view would you query to find out information about free extents in your database? Write a query to display a count of the number of free extents in your database?
 We can use scripts. Exactly its difficult to know

47) Write a query to display the tablespace name, datafile name and type of extent management (local or dictionary) from the data dictionary?
You need to combine dba_data_files and dba_tablespaces

48) Which two types of tablespace cannot be taken offline or dropped?

49) When a tablespace is offline can it be made read-only? Perform the
Required steps to confirm your answer?
 Didn’t got the answer

50) Which parameter specifies the percentage of space in each data block that is reserved for future updates?
51) write down two reasons why automatic extent allocation to an extent may fail?
If the disk space reached max limit
If autoextend reached maxsize limit

52) Query the DBA_CONSTRAINTS view and display the names of all the constraints that are created in the CUSTOMER table?
 Select constraint_name from dba_constraints where table_name=’CUSTOMER’;

53) Write a command to display the names of all BITMAP indexes created in the database?
 Select index_name from dba_indexes where index_type=’BITMAP’;

54) Write a command to coalesce the extents of any index of your choice?
Alter tablespace coalesce;
Don’t know for extents

55) . What happens to a row that is bigger than a single block? What is this called? Which data dictionary view can be queried to obtain information about such blocks?
 Row will be chained into multiple blocks. CHAINED_ROWS is the view

56) Write a query to retrieve the employee number and ROWIDs of all rows that belong to the EMP table belonging to user SCOTT?
 Select rowid,empno from scott.emp;

57) During a long-running transaction, you receive an error message indicating you have insufficient space in rollback segment RO4. Which storage parameter would you modify to solve this problem?
 Repeated question

58) How to compile a view? How to compile a table?
 Alter view compile;
Tables cannot be compiled

59) What is the block size of your database and how do you see it?

60) At one time you lost parameter file accidentally and you don’t have any backup. How you will recreate a new parameter file with the parameters set to previous values.?
We can recover it from alert log file which contains non-default values

61) You want to retain only last 3 backups of datafiles. How do you go for it in RMAN?
By configuring backup retention policy to redundancy 3


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