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Top 20 Oracle DBA Interview Questions and Answers

Published On: June 10, 2024

Oracle DBA Interview Questions and Answers

Expert technical knowledge and hands-on database management experience are prerequisites for becoming an Oracle DBA. As database performance is so critical to firms, DBAs are being hired frequently to monitor it. The top 20 Oracle DBA interview questions and answers are provided here to help you land a job with just one try.  

Oracle DBA Interview Questions and Answers for Freshers

1. How do you define Oracle?

Oracle is a well-known technology business that creates software services and data management systems. Oracle DBA is one of the company’s key products, used by numerous other enterprises for data management and storage.

2. What is a database?

An information-containing collection of data records, typically in the form of tables, is called a database. We can simply access and update data records thanks to it. Databases are useful for administering HRMS (Human Resource Management System) and other systems in large enterprises.

3. Why use the index in a database?

Indexes are employed in databases to provide easy access to and retrieval of data. When it comes to enhancing query performance, indexes are crucial. They make it possible for the database to quickly locate and execute any given row and column.

4. Define tablespace.

One definition of tablespace is the logical storage unit. It permits combining many data files into groups. It helps with database object storage allocation and organization.

5. How does the B-tree index function?

Because of the B-tree index, the database has sorted every value in the table. Next, a B-tree data structure is used to hold this information. 

Pointers to every row in a table are contained in this data structure. The way all of the values in this structure are kept makes searching for and retrieving data quite easy. 

6. What source offers details regarding the DBA segmentation?

“DBA_segments” in DBA provides the segment information. Logical storage units are one way to characterize the segments. Data, including tables, partitions, and indexes, make up these structures.

7. What distinguishes logical storage from physical storage?

Logical and physical storage are essential components of the Oracle database architecture. Files in the database are included in the physical storage. On the other hand, segments, blocks, tablespaces, and so forth make up logical storage.

8. What does the normalization of databases mean?

The practice of organizing data within a database is known as database normalization. Data redundancy can be decreased with the use of normalization. It enhances data integrity as well. Normalization eliminates the inconsistent dependency, making the database more adaptable.

9. What distinguishes data chunks and extents from one another?

The storage units are the extents and data blocks. They permit the information to be kept in the database. Their sole difference is the amount of data they can store. 

The smallest logical storage unit is called a data block. Thus, it has a designated area.

Conversely, an extent is a collection of data chunks. It can store one or more data blocks. Segments receive the extent as a unit.

10. Why are rollback segments used?

The transactions are rolled back using the rollback segment. Rollback segments can be present in a database in one or more instances. 

It is also beneficial for putting the database transaction control mechanism into practice. because it enables the database to save the undo data that was created while the transactions were running.

Oracle DBA Interview Questions and Answers for Experienced

11. What is the difference between cluster and non-cluster indexes?

There are two sorts of indexes: clustered and non-clustered. Their information storage methods are the only ones that differ. 

  • The clustered index stores the table physically. Records are kept in order via a clustered index. As a result, we may state that it only has one clustered index. 
  • A non-clustered index employs logical sorting. In this case, the row order does not correspond to the actual data’s physical order.

12. Define the DBA’s responsibilities.

Database administrators are responsible for a wide range of tasks. The following are a handful of them:

  • Database performance is enhanced with DBA.
  • The DBA assists with storage and object management for databases.
  • The database administrator contributes to maintaining database security.
  • The DBA permits the addition of new users, the deletion of current users, changes to user permissions, and more.

13. How can we determine the database’s total size?

The following views will provide you with information regarding the size of the database:

Dba_segments: The DBA_segments is where segment information is stored in DBA. Data, including tables, partitions, and indexes, make up these structures. 

v$log: The v$log is a useful tool for learning about redo log files. When system failures and mistakes, the redo log files are crucial since they enable data recovery.

Dba_data_files: This table is used to give details regarding the space allotted to datafiles. The tablespaces in question are permanent.

14. What are Oracle Database Security Management’s primary features?

Oracle database security has a lot of features. Some of them are:

  • Data access can be managed with the use of Oracle database security.
  • It verifies the user’s details to prevent unrestricted users from quickly accessing the data.
  • The data in the Oracle database is safeguarded.

15. What does the term “scope parameter” mean to you?

When utilizing the server parameter file or the file, the scope parameter specifies how modifications to a value impact the database. There are three distinct scopes with which we can modify parameter values:

Spfile scope: In this case, the modifications take effect at the subsequent database reboot.

Memory scope: In this case, modifications are made instantly in memory and are gone upon database restart.

Both scopes: Instantaneous updates are made in RAM, where they stay even after the database is restarted. 

16. What does a password file serve as?

The data dictionary of the database stores the user’s credentials. It checks the user’s account and passcode to the information in the database when the user tries to seek access to it. 

  • Once Database access is only granted to the user if the passcode and account match. As long as the database is open, we can access the data dictionary. 
  • The admin credentials are also contained in this dictionary. Once the database is shut off, you are unable to access the dictionary. 

One of the responsibilities of the executive is to restart a closed database, so even in the event of a server failure, administrators must be able to access the database.

An isolated operating system file stored on a disc and unconnected to the server is called a password file. 

It keeps track of SYSDBA and SYSOPER customers’ login credentials. The password file is used to validate admins with those rights even when the database is not online.

17. What is a control file exactly?

  • The actual data from the database is contained in two parts of this file.
  • With the help of the control file, you can eliminate the possibility of crashing.
  • It includes details about the duration, checkpoint, database name, and whether or not there are numerous log files.
  • The CONTROL FILE argument stores information about the control file, making it easier to locate.
  • To avoid problems arising from corrupted files, it is advisable to make multiple copies of the control file.

18. How can one use the ANALYZE command?

  • It is employed to obtain object statistics from the optimizer and save them in the database.
  • It is employed to eliminate data regarding the data that the database uses from the database.
  • It is employed to guarantee the accuracy of the object’s structure.
  • It is used to retrieve the linked and imported rows for the table or cluster.

19. Why are writes to LGWR coming before writes to DBWR?

In general, transaction processing is less important than transaction recordkeeping. Let’s say there are several entries on the disk and there is a power outage. 

The redo logs on the disc can then be retrieved to recover the transactions. Using this strategy, temporary blocks are transferred to storage once redo logs are made durable.

20. What phases does an instance go through when it’s first starting up?

You can use the following modes to launch a database:

NOMOUNT: The initial phase. The instance is started in this way.

MOUNT: The second phase is this one. The database is mounted and the instance is started in this mode. You are unable to access data, though, as the database is not accessible. At this point, though, you can complete many maintenance tasks.

OPEN: The last phase is this one. All of the data is available and the database is open. As “read/write” is the default open mode, you can either read or write to the data. It is also feasible to open it in “read-only” mode, which restricts your ability to modify the data to just reading it. 


Thrive in your DBA interviews by reviewing your skills with these Oracle DBA interview questions and answers crafted by SLA experts. Hone your skills with our Oracle DBA training in Chennai.

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