Oracle DBA Interview Questions and Answers

Oracle DBA Interview Questions

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Best Oracle DBA Interview Questions and Answers

Are you in search of the best Oracle DBA Interview Questions and Answers? Do you wish to crack every Oracle DBA interview that you are going to attend? If you’re nodding your head for these two questions then you have arrived at the right place! At CourseJet we have committed to help the students with the frequently asked Oracle DBA interview questions and answers. Preparing these top Oracle DBA interview questions and answers would help you in acquiring the knowledge and confidence to clear your Oracle DBA interview.

All these top Oracle DBA interview questions are grouped hereafter deep research. These Oracle DBA interview questions cover all the concepts from the essential areas of the DBA which include Oracle Database Architecture, DML and DCL operations, Oracle DBA installation, recovery manager, Oracle database parameters, RDBMS to store and retrieve data, etc. 

Oracle DBA is a popular database management system developed and owned by Oracle corporation. This database is typically used for data warehousing, for running online transaction processing, and for handing the mixed database workloads.  These top Oracle DBA interview questions and answers are suitable for both freshers as well as experienced candidates. 

Frequently Asked Oracle DBA Interview Questions

All these Oracle DBA questions are covered right from the basic to advanced level. All these interview questions are suitable for the professionals like Software Developers, Database Analysts and Administrators, SQL Programmers and Architects, Project Managers, and freshers who wish to build their career in the database management world. Mastering these lists of frequently asked interview questions will definitely help you for exceptional performance in the Oracle DBA interview. 

In modern times, data storage has become an essential task for organizations. To manage the huge data sets and ever-growing data, organizations are looking for the certified Oracle DBA professionals. If you are about to start your career in the Oracle DBA then you have a great career ahead with a good scope.  All these Oracle DBA interview questions and answers cover from the basic to advanced level areas.  Preparing these Oracle DBA interview questions for freshers and experienced will definitely help you in getting into your dream career.  Without wasting no time let’s get into the best Oracle DBA interview questions and answers part.  

Oracle DBA Interview Questions for Freshers

Following are the list of frequently asked Oracle DBA interview questions and answers

1. What is Oracle DBA?

Oracle DBA is a popular database management system developed and owned by Oracle corporation. This database is typically used for data warehousing, for running online transaction processing, and for handing the mixed database workloads. Oracle database acts as the best tool for managing all types of data.  

2. What is the difference between Oracle DBA and Oracle Developer?

The following table gives you a clear view of the core differences between Oracle DBA and Oracle Developer. 

Oracle DBA

Oracle Developer 

Manage Databases

For coding and development 

Database maintenance

Database development

Streamlined tasks

Wide Range tasks 

Works in  backend database management 

It is used for front end development  

It also performs  recovery, Backup, Server connectivity, and much more 

Other areas it works are designing, coding, UI, etc.  

3. Explain four possible ways to execute an SQL query on an oracle database?

The following are the four possible ways in which we can execute a query on the Oracle database.
  • By using a GUI (Graphic User Interface) tool like SQL developer. This tool allows direct execution of SQL commands.
  • By deploying the SQL*Plus command-line tool. This tool enables you to execute any type of SQL commands directly.
  • By writing your own program: It is one of the widely used and conventional ways for executing a SQL query. Any windows or web program that uses the Oracle database can execute SQL queries. You can use programming languages such as Java, and .Net to execute SQL commands and the language should have a driver to access the database.
  • Oracle Enterprise Manager: It also helps you in the execution of an SQL query. This is also called the indirect way to execute a query. Using Oracle Enterprise Manager you can perform certain tasks and these tasks are transformed into SQL queries and these queries are ultimately executed against the database.

4. What is Oracle?

Oracle is a multinational computer technology corporation and provides database server facilities in a structured way. It creates an environment where users can store and retrieve data. It also allows multi-user access to the same database without any intersection. Oracle provides a highly secured database environment to prevent the hacks, data loss and gives you a seamless data recovery option. Oracle gives you a high performance to execute all types of tasks against the database. 

5. What do you know about SQL *Plus and what role does it play in Oracle DBA?

Oracle SQL*Plus is a command-line tool offered by Oracle corporation. You need not pay any fair for getting this tool.  It comes as a default tool along with Oracle database installations or client installations. After finishing the oracle database installation on a system you can easily spot it below the “$ORACLE_HOME/bin/” directory.   Using SQL*Plus you can easily connect to a database and execute SQL queries or SQL commands against the connected database. Moreover, SQL*Plus comes with some inbuilt commands which help you in formatting the output and makes the results clear.  

6. What is Oracle Database?

Oracle is a topmost and specialized software corporation that helps you to develop and manage your data. The database consists of logical and physical structures in which users can store the entire data.  The software is used to manage the database is called an Oracle Database server.  All these tasks performed on a physical database system are called an Oracle Database system.  

Oracle Database also comes with advanced features to make the data management simpler and more secure than ever before. In Oracle Database buffer cache stores the data in memory and enables quick access. Oracle redo logs will help you to track the changes made to a database. Data Guard helps you in protecting your organizational data and control the structure of the data.  

7. What is an Oracle Index?

An index is a Schema object that helps you with an entry for every value that appears in columns(s). It is an optional option associated with a table that gives you clear access to rows. Oracle Index also helps in improving the performance of the data retrieval data process. You can create an index on multiple columns of a table. Oracle Database supports multiple types of Index. 

8. What are the various roles performed by a DBA?

In general, a DBA has the authority to eliminate the existing users, add new users, modify any of the environment, and can modify the privileges added to the users. Following are the list of tasks performed by a DBA:
  • User and security management
  • Database management
  • Control and monitor database performance
  • Manage Schema objects
  • Schedule and automate jobs
  • Perform backup and recovery

9. Explain the different Oracle Database objects?

The different oracle database objects are:
  • Tablespaces
  • Sequences
  • Synonyms
  • Indexes
  • Views
  • Tables

10. State the benefits of ORDBMS?

The ORDBMS allows the objects to store as they are. It simplifies the way to connect with the DBA language to any Object Oriented Programming language.  Sometimes the language may be the same one used in application development. It eases the task of developers and they need not have two representations of objects. 

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11. What are typical tasks performed by an oracle DBA?

As an Oracle DBA developer one has to perform the below tasks:
  • Oracle Software installation
  • Performing upgrades of the database
  • Creating oracle databases
  • Starting and stopping the database
  • Managing users and security
  • Controlling database storage structures
  • Database backup and performing database recovery
  • Managing schema objects such as Views, indexes, and tables
  • Frequently monitoring the health of the database and developing measures to handle as required.
  • Performance tuning and monitoring
In a small or medium-sized organization, all the above tasks can be performed by a single DBA. When it comes to large corporations all these tasks are divided into departments and performed by several DBAs with a title called Database Tuning Expert, Database Security Administrator, etc.

12. What are the tools available for administering the database?

Below mentioned are some of the tools, products, and utilities to make the database administration more efficient:
  • Database Configuration Assistant (DBCA): It is capable enough to develop a database by utilizing the templates supplied by Oracle, or one can also develop their own templates. In such scenarios it allows us to copy a preconfigured seed database, which saves us a great amount of time and effort in customization and developing a database from the ground level.
  • Oracle Universal Installer (OUI): It enables the users to install the Oracle software. Oracle Universal Installer automatically launches the database configuration assistant to install the database.
  • Database Upgrade Assistant: This tool acts as a guide to upgrading the existing database to the new database version.
  • Oracle Net Manager: It acts as a guide to achieving network configuration goals.
  • Oracle Enterprise Manager: Oracle Enterprise Manager acts as a primary tool for managing databases.  Once we are done with tasks such as oracle software installation,  database up-gradation, network configuration, and the very next thing is to use the Oracle Enterprise Manager which acts as an interface for managing a database.  In addition to providing an interface for managing the database it also acts as an interface for Oracle utilities and performance advisors.

13. What do you know about the architecture of Oracle Grid?

The Oracle Grid is a software that provides system support for Oracle database including automatic restart capabilities, file system management, and volume management.  

The oracle Grid architecture brings all the huge number of networks, servers, and storage into an on-demanded, flexible resource for meeting the enterprise computing needs. Grid computing acts as a controller for analyzing the need for resources and adjusting the supply to meet the demand. 

Grid computing utilizes an advanced workload management system that enables applications to distribute/ share resources across the servers. It also adjusts the data processing capacity based on the requirement and also the resources within a location dynamically supplied. The grid helps web services to quickly integrate applications that create new business processes.  

14. Explain the difference between the SPFILE and PFILE?

  • PFILE: It is a text parameter file and supplies the data for configuring the database initialization parameters.
  • SPFILE: It consists of all the data required for configuring the database initialization parameters. SPFILE allows us to make dynamic changes without any need to reset the instance.

15. Who takes the responsibility to update the indexes? 

Oracle looks after the task of updating indexes. It automatically maintains indexes and if any change is made to the table data Oracle instantly updates it to relevant indexes.

16. What is meant by Synonym in Oracle terminology?

A Synonym acts as an identifier and helps in referencing other database objects in an SQL statement. Following are the list of database objects to which Synonym can be created are:
  • View
  • Table
  • Sequence
  • Another synonym

17. What is meant by password file and why do we need it?

All the passwords and usernames given to the users are stored in the data dictionary of a database. Each time the user wishes to log into the database, the assigned user name and password to a user can be checked against the data stored in the dictionary and if the values match then the users get access to the database. The data dictionary is an integral part of the database and available as long as the database is open. All the usernames and passwords are given to administer also managed by this dictionary. 

If in case the database is closed automatically the data dictionary will also stop functioning  and you no longer have access to it.  In such scenarios, we need a solution for administrators to logon to the database even when the database is down.  Here comes the Password file which is a unique operating system file that has been stored on a disk out of the database. Whoever the users having SYSDBA or SYSOPER privilege for their username and password gets stored in the password file. Users or administrators who have this privilege can access the password file even if the database is down. 

18. What are the differences between the Oracle DBA role and Oracle Developer role?

  • Oracle DBA Role: The Oracle DBA’s main role is to conduct database administration that is associated with functionalities such as regular database maintenance, enforcing security policies, data backup, and recovery, and a lot more other tasks. Even though the DBA’s are not supposed to develop any code they should have PL/SQL and SQL knowledge to administer the database effectively.
  • Oracle Developer Role: The major duty of an Oracle developer is to develop backend applications. They develop data models according to business nature and needs. They also design tables, develop indexed and other types of constraints. Oracle Developers are expected to have sound knowledge of languages like SQL and PL/SQL. They are not expected to perform the tasks related to database administration tasks.

Based on the structure of an organization, sometimes the DBA’s might also be asked to perform basic development tasks and need to coordinate with developers to achieve the common goal.

19. What are the elements to specify in the SQL script while developing a database?

We can also develop a database using an SQL script.  Below mentioned are the elements one should specify while developing a database using SQL scripts.
  • Database name
  • The SYSTEM user password
  • The SYS user Password
  • Minimum three online redo log groups
  • Specify a minimum of two members for each redo log group
  • National character set and Character set of the database.
  • Location and size of the SYSTEM
  • Specify normal tablespace
  • SYSAUX tablespace
  • Normal tablespace and temporary tablespace
  • Specify an undo tablespace.

20. What makes up an Oracle Instance?

An instance is developed from a distributed memory region on RAM known as System Global Area and background process. As SGA is a shared memory it can be accessed by multiple processes and holds the data needed to operate an instance. The background processes and   System Global Area when the instance is “started”.  If you “shut down” the instance the all processes associated with it get killed and the shared memory region will go back to the operating system.

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21. What does an Oracle database consist of?

An Oracle database stays on a permanent disk. It consists of various files and these files are broadly categorized into three types:
  • DataFiles: All the DataFiles store “user” data or “system” data. The data related to an application is defined as a “user” data.  The best example of a “system” data is “data dictionary”.
  • OnlineRedo Log Files: This file acts as a place for holding “change” records. All the changes done to a data file will be first written to online redo log files.
  • ControlFiles: These types of files are very small in nature when compared to the above files. Though the ControlFiles are small in nature they play a vital role.  They are responsible for holding the data related to physical structures of the database like online redo log files, location of data files, etc.

22. What are the tools used for starting an Oracle database?

You can use any of the following tools to startup a database:
  • SQL*Plus: It is the commonly used option for starting an Oracle database. All you need to do is connect to an idle instance with SQL*Plus and use the startup command to start the instant.
  • Oracle Enterprise Manager: This is also one of the widely used tools to start a database. You can have the chance to access the Oracle Enterprise Manager even if the database is stopped.  OEM will help you in finding the status of a down database and will give you the startup button.
  • RMAN: It is one of the least used tools for starting a database. Using the Recovery Manager command line you can easily start a button.

23. What are the stages in which an instance passes through while starting?

Following are three stages in which an instance pass though:
  • NOMOUNT: It is the very beginning place where the instance gets stored.
  • MOUNT: At this stage, the instance gets started and the database is mounted. At this stage, you can not access the data because the database is still not open. You can execute multiple maintenance tasks at this stage. But you get the choice to perform several maintenance tasks at this stage.
  • OPEN: It is the last date on which the database is open to access and you can have access to all the data. At this stage, you will get a default mode for “read/write” this means you can perform read/ write tasks. But most probably at this stage, you get a read-only option and you are not allowed to make any changes to data.

24. How can you prevent a user from accessing data while the database is under maintenance?

All the users who have a CREATE SESSION” privilege can make a connection when the database is open. The database can be opened in a “restricted” mode and in this mode, only users with the “RESTRICTED SESSION” facility can access the database. This facility is allowed to only DBAs and not to the regular users. Restricted mode is the best possible way to prevent users from accessing data when it is under maintenance.   

25. What are the different modes to shutdown a database?

Following are the four typical ways to shut down a database:
  • Normal: In this scenario, no new connections are allowed to access the database and the database gets automatically shut down once all the sessions disconnect themselves.
  • Immediate: In this mode, no new connections are accepted and the current transactions are rolled back. Even the changes made by an active transaction will also be lost.
  • Transactional: In this mode, not even a single new connection is accepted and Oracle waits until all the active sessions are completed.
  • Abort: It makes the database to shut down immediately even though the database is not shut down neatly. This process is rarely used one because the database has to perform instance recovery whenever it starts.

26. What is the information that can be furnished while developing a sequence?

Following is a list of information one has to furnish while creating a Sequence:
  • Name of the Sequence: It represents the Schema, should be unique, and resides inside a schema
  • Start With: It will be a number with which a sequence gets starts
  • Increment by: this represents how much an increment should be increased at every move.
  • Nocycle: It will define the Sequence whether it should begin from the start once it reaches the end.
  • Nocache: It shows how much a next sequence will be cached in SGA. Noche means there will be no next sequence that will be cached.

27. How is it possible to automatically restart the database once the reboot of the server is over?

In the default configuration, there is no pre-configuration for starting the Oracle database automatically after the server reboot finishes. In general, you need to start it manually after finishing the reboot.  If you wish to start the database automatically after a server reboot there are two methods to do it:
  • Using Oracle Restart: Using an advanced feature of Oracle High Availability Service called “Oracle Restart” feature.
  • Writing Your Own Script: You can also make it possible by writing a “bash” script to the database and integrating that script for starting the operating system.

28. What are the major differences between a Dedicated Server Architecture and Shared Server Architecture?

Dedicated Server: When a user has an access to a database, he can send the queries for the purpose of execution. All the SQL queries are executed by a “server process” and the output is rolled back to the user.  In a dedicated Server architecture the server will create one server process for each user. And that specific process is dedicated to a particular client and will not serve others. When it comes to “ shared server” architecture, only one server process will execute multiple clients’ requests. The total memory consumption is very less in shared server architecture compared to dedicated architecture. But some of the major operations like DBA tasks can only be executed by a dedicated server.

19. List the instance parameters being used in configuring the shared server architecture?

Following are the list of parameters being used in shared architecture
  • DISPATCHERS: A string value used to configure dispatchers.
  • SHARED_SERVERS: This parameter specifies the least number of shared server processes that are presented in a server.
  • MAX SHARED_SERVERS: This parameter explains how many shared processes can be run at a given point in time.
  • SHARED_SERVER SESSIONS: This parameter explains the highest number of sessions that can be run at a time using a shared connection.
  • CIRCUITS: This parameter defines the maximum number of virtual circuits that can be presented in the system.

30. How does the “Database Writer” process work?

We can have a larger number of database background processes and are termed as “DBWn” on the operating system.  This process is mainly used for writing the “dirty” buffers to a disk. There are times where a data block needs to be updated. The other name for the modified database block is called the “dirty” block. 

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31. What is the main purpose of the Index?

The major purpose of indexing is used for increasing the performance of the retrieval process. In order to make the index we use one or multiple rows.  The index helps in slowing down the performance of insertion and improves the data retrieval process.

22. Define table in Oracle?

The tables are the basic unit of data storage and used for storing the data in the Oracle database. Oracle majorly uses a wide range of tables to store the data in an organized way into rows and columns of a table. Each table has unique name and columns headings such as employee name, employee ID, the role performed, etc.

33. What is View?

A View is defined as a virtual table in the Oracle database because you can make use of this table in your SQL queries. Each view comes with columns with different data types so you can perform a query against a view or manage their contents using UPDATE, INSERT, MERGE, and DELETE statements. It works similarly to a table but it does not store any data. A view is also termed as a named query stored in the database. Whenever you query a data from the view, Oracle uses this stored query to get back the data from the underlying tables.

34. What is meant by row changing in Oracle Database?

Usually, Row changing happens when the row is too big to fit into a single data block when it is inserted for the first time.  In such scenarios, Oracle stores the data of a particular row into a chain of blocks assigned for that segment.  Row changing tasks usually happens when the larger Rows contain a column datatype such as LOB, LONG, LONG RAW, etc.  These are also called unavoidable cases.

25. What is meant by “Extent”?

An Extent is defined as a group of contiguous blocks allocated in a database. In the Oracle database program, the initial group of contiguous blocks are created when a segment is created and this is also called an initial extent.  Once the initial extent is filled, the program list of other extents automatically and these are also called as next extents. The total number of extents that can be added depends on the available storage space and also some cases by the program used.

36. What is Datafile in Oracle?

It is a large unit of physical storage in the Operating System file system. All the Oracle data files are combined together to provide the physical storage and construct a single Oracle tablespace. The data file helps the users to store tables and indexes allocated to the database. Each database consists of one or more than one data file.

37. What do you know about the Redo log?

Redo log plays an important role in executing data recovery operations and consists of two or more preallocated files that are intended to record all changes made to the database. Every instance of an Oracle database consists of a redo log and provides security when an instance fails.

38. What are the major elements contained in a control file?

Each database consists of a control file. It is a little binary file that stores the physical structure of a database and consist of the following elements:

  • Name of the database
  • Names of online redo log files and data files
  • The sequence number of the current log
  • The timestamp of a database creation
  • Checkpoint information

39. What are the benefits of using control files?

Control files play an important role in the effective management of Oracle database servers. You must need an available control file for any query into the Oracle database. It is difficult to mount the database that can not be mounted and recovery becomes a highly challenging task. You need to develop control files when you wish to alter the configurations in the control files.

40. Why do we use the SELECT statement?

The SELECT statement is typically used for the selection of targeted values from a table that is stored in a database. In Oracle, the SELECT statement is being used for the purpose of retrieving data from one or more tables from an Oracle database.

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41. How many types of SQL statements are there?

We have five major types of SQL statements which are:
  • Data Manipulation Language,
  • Data Definition Language,
  • Session Control
  • Transactional Control,
  • System Control.

42. What is meant by the transaction in an Oracle database?

A transaction is defined as the sequence of SQL statements and all these statements are considered as a single unit of work in the Oracle database.  Oracle supports the transactions that are defined by the SQL standard. When you connect to a database the transaction begins automatically. When a transaction begins working, all the SQL DML statements you issue becomes a part of the specific transaction. A transaction automatically ends when you get disconnected from a database, or when you issue commands like ROLLBACK or COMMIT.

43. Define GROUP BY?

It is an aggregate function such s MULTIPLE, SUM, etc. With the absence of this GROUP BY function SUM for individual values can not be calculated.

44. What is SQL?

SQL is abbreviated as a structured query language that is specially designed and developed for managing data in RDBMS. Its scope includes query, data insert, schema creation, update, delete, and control data access.

45. What is a Private database link?

This type of link is specially created for an individual user. It can be used when the owner of the link configures a global object name in an SQL statement or, in procedures, or in the definition of the owner’s views.

46. What is a Public database link?

A  database link is nothing but a schema object of a database that helps in accessing the objects in other databases. If you create a database link with a Public clause it can be available for all the users.

27. What are the areas in which we can perform Tuning?

Following are the areas in which a user can perform tuning:
  • Memory Allocation.
  • Database Design.
  • Database Contention.
  • Disk I/Os.
  • OS level (CPU).

48. Explain the disk components available in the Oracle database?

Following are the list of disk components:
  • Parameter files
  • Password files
  • Control files
  • Redo Logs
  • Data files

49. What is Checkpoint in Oracle in Database?

The checkpoint process is mainly used for updating the file headers in the database datafiles. In general, a checkpoint takes place when Oracle transfers updated blocks or new blocks from the RAM buffer cache. The Checkpoints in oracle keeps the database data files and database buffer cache synchronized. Synchronization is an advanced mechanism used by Oracle to ensure that a database can always be recovered.

50. Name the different types of backups available in Oracle Database?

Following are the typically used database recovery modes:
  • Cold backup
  • Datapump, Exp/IMP
  • RMAN

51. What are the different types of Checkpoints?

Following are the various types of Checkpoints:  
  • Full ckpt
  • File-level ckpt
  • Thread ckpt
  • Incremental
  • Object-level
  • log switch

With this, we have come to the end of the frequently asked Oracle database interview questions and answers for freshers and experienced candidates’ blog. Preparing these Oracle database top interview questions would definitely help you in clearing your interview in the very first attempt. Hope you have found this blog useful. Stay tuned to this blog for the latest Oracle database interview questions and answers. Happy learning!

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