Database Administrator (DBA) Interview Questions

This post is a curated collection of top-notch interview questions tailored for Database Reliability Engineer (DBRE) applicants.

Whether you’re a seasoned DBA refining your expertise, an interviewer on the quest for valuable questions, or a hopeful candidate gearing up for a pivotal DBRE interview, these thought-provoking queries are meticulously crafted to ignite insightful conversations and deepen your understanding of SQL Server’s dynamic landscape.

Hope you enjoy!

1. Diagnosing Poor SQL Server Performance

Question: What are some common checks we can do to diagnose a SQL Server that suddenly starts to perform poorly?

Answer:

Review SQL Server logs for errors.
Analyze wait statistics.
Check for blocking processes.
Examine query execution plans.
Monitor server resources: CPU, memory, and disk usage.

Bonus Points: Emphasize the importance of regularly monitoring and addressing these aspects to maintain optimal performance.

2. Navigating System Tables for Database Insights

Question: What system tables would you check to view database file paths or database meta properties (e.g., autoshrink, recovery model)? Extra points if you know the difference between sys.databases & sys.database_files.

Answer:

Use sys.databases for overall database properties.
Utilize sys.database_files for file-specific details.

Bonus Points: Understanding the distinction between sys.databases and sys.database_files showcases a deeper knowledge of SQL Server internals.

3. Confirming Table Participation in Replication

Question: How would you check if a table is part of SQL Server Replication?

Answer: Execute the query:

SELECT * 
FROM sys.tables 
WHERE name = 'YourTableName' 
AND OBJECTPROPERTY(object_id, 'TableHasReplicationFilter') = 1;

Bonus Points: Highlighting the specific query for checking table replication demonstrates practical knowledge. Further explaining the Replication technology while answering is a bonus (e.g. mentioning reliability of data to Subscribers, or Publications/Subscriptions/Distributor).

4. Identifying SQL Server’s Always On Availability Group Membership

Question: How would you know if a SQL Server is part of an Always On Availability Group?

Answer: Execute the query:

SELECT replica_server_name 
FROM sys.dm_hadr_availability_replica_states;

Bonus Points: Showcasing familiarity with the specific query for identifying availability group membership adds value.

5. Efficient Stored Procedure Execution Scheduling

Question: How would you schedule the execution of a Stored Procedure?

Answer: Utilize SQL Server Agent Jobs to create a job, add a step to execute the stored procedure, and set the desired schedule.

Bonus Points: Highlighting the use of SQL Server Agent Jobs demonstrates practical knowledge of automation.

6. Ensuring Correct Index Usage for Query Optimization

Question: You have a query that is taking a long time to execute. How can we ensure it’s using the correct index?

Answer: Utilize the SQL Server Query Execution Plan to examine which indexes are being used. Ensure that indexes are properly designed, updated, and cover the columns involved in the query.

Bonus Points: Emphasizing the importance of proper index design and maintenance adds value to the answer.

7. Impact of WITH (NO LOCK) on Query Results

Question: Explain what adding WITH (NO LOCK) does to a query and result.

Answer: Adding WITH (NO LOCK) allows for a dirty read, reading uncommitted data. It enhances performance but may result in reading inconsistent data.

Bonus Points: Highlight the trade-off between performance and data accuracy when using WITH (NO LOCK).

8. SQL Server Backup Strategies: Explain the Importance of Differential Backups.

Question: Explain the importance of differential backups in SQL Server backup strategies.

Answer: Differential backups capture changes made since the last full backup, reducing backup duration and storage requirements.

Bonus Points: Emphasize the role of differential backups in optimizing backup processes.

9. SQL Server Security: How Do You Grant Execute Permissions on a Stored Procedure to a Specific User?

Question: How do you grant execute permissions on a stored procedure to a specific user in SQL Server?

Answer: Use the GRANT EXECUTE statement: GRANT EXECUTE ON YourStoredProcedure TO YourUser;

Bonus Points: Highlighting the precise SQL statement for granting execute permissions showcases efficiency.

10. Disaster Recovery Essentials: Outline the Steps to Restore a Database from a Full Backup.

Question: Outline the steps to restore a SQL Server database from a full backup.

Answer: Use the RESTORE DATABASE command: RESTORE DATABASE YourDatabase FROM DISK = 'YourBackupFile.bak' WITH REPLACE, NORECOVERY;

Bonus Points: Detailing the specific command for database restoration adds practical value.