SQL Server Database Administrator with 6 years of experience, interview questions

For an L2 SQL Server Database Administrator with 6 years of experience, interview questions will typically focus on real-time scenarios, problem-solving skills, and advanced SQL Server concepts. Here are some questions that might be asked:

Here are sample answers to each of the questions provided:

Performance Tuning and Optimization

1. Describe a situation where you had to troubleshoot a slow-running query. What steps did you take to identify and resolve the issue?
   • Answer: I once encountered a slow-running query that impacted an application’s performance. First, I examined the query’s execution plan to identify bottlenecks. I found a table scan that could be optimized with proper indexing. After adding the index, I re-evaluated the query performance, resulting in a significant improvement.
2. How do you use execution plans to diagnose query performance problems?
   • Answer: Execution plans help me understand how SQL Server processes a query. I look for costly operations like table scans, index scans, and sorts. By analyzing the plan, I can pinpoint inefficiencies and optimize queries through indexing, rewriting queries, or updating statistics.
3. What are some common causes of deadlocks in SQL Server, and how do you resolve them?
   • Answer: Common causes of deadlocks include long-running transactions, inconsistent access order to resources, and insufficient indexing. I resolve deadlocks by ensuring transactions are short, accessing resources in a consistent order, and adding appropriate indexes. Monitoring and using deadlock graphs also help in identifying and resolving deadlocks.
4. Explain how you would approach indexing a large table. What factors would you consider?
   • Answer: When indexing a large table, I consider the most frequent queries and their filtering conditions. I create indexes on columns used in WHERE clauses, joins, and aggregations. I also balance between the benefits of the index and the overhead of maintaining it, ensuring not to over-index which can slow down DML operations.
5. How do you monitor and improve the performance of SQL Server databases in real time?
   • Answer: I use SQL Server Profiler, Extended Events, and Performance Monitor to track performance metrics like CPU usage, memory usage, and disk I/O. I also set up alerts for threshold breaches and analyze slow-running queries using DMVs and query performance insights.

Backup and Recovery

6. Can you walk me through your process for setting up and verifying a backup strategy for a critical database?
   • Answer: I establish a backup strategy based on RPO and RTO requirements. Typically, it involves full backups nightly, differential backups hourly, and transaction log backups every 10-15 minutes. I regularly test backup restores to ensure data integrity and that the recovery process meets business requirements.
7. Describe a situation where you had to perform a database restore. What challenges did you face, and how did you overcome them?
   • Answer: I had to restore a production database due to accidental data deletion. The challenge was minimizing downtime. I restored the latest full backup followed by differential and transaction log backups. To expedite the process, I used backup compression and redirected the restore to a secondary server.
8. How would you handle a scenario where a transaction log file grows unexpectedly large?
   • Answer: First, I would check if a transaction is holding the log file open. If so, I’d identify and terminate the transaction if appropriate. Then, I’d ensure regular transaction log backups are happening. If necessary, I’d shrink the log file to a manageable size and investigate the root cause to prevent recurrence.

High Availability and Disaster Recovery

9. What are the different high availability options available in SQL Server?
   • Answer: High availability options in SQL Server include Always On Availability Groups, Failover Cluster Instances (FCI), Database Mirroring (deprecated), Log Shipping, and Replication. Each has its use cases depending on the required RPO and RTO.
10. How do you set up and manage a SQL Server Always On Availability Group?
    • Answer: Setting up Always On Availability Groups involves configuring Windows Server Failover Clustering (WSFC), preparing the SQL Server instances, and creating the availability group with primary and secondary replicas. I manage it by monitoring the health of replicas, ensuring synchronization, and testing failover procedures regularly.
11. Can you describe a time when you had to implement a disaster recovery plan? What steps did you take to ensure minimal data loss and downtime?
    • Answer: Implementing a disaster recovery plan involved setting up a secondary site with log shipping. During a primary site outage, we switched to the secondary site by applying the latest logs and redirecting applications. Regular DR drills ensured that the plan was effective, with minimal data loss and downtime.

Security and Compliance

12. How do you manage and enforce security policies in SQL Server?
    • Answer: I enforce security policies by implementing the principle of least privilege, using roles and permissions appropriately, and ensuring strong password policies. I also use Transparent Data Encryption (TDE) and monitor login attempts and security audits.
13. What steps do you take to ensure data encryption in SQL Server?
    • Answer: For data encryption, I use Transparent Data Encryption (TDE) for encrypting data at rest, and SSL/TLS for encrypting data in transit. Additionally, I use Always Encrypted for sensitive data and ensure proper key management practices are in place.
14. Explain how you handle permissions and roles within a SQL Server environment.
    • Answer: I manage permissions by creating roles with the necessary permissions and assigning users to these roles. This ensures consistent and manageable security. I regularly review permissions and roles to ensure they are aligned with current requirements and least privilege principles.

Real-Time Scenarios

15. A user reports that they are unable to connect to the database. How do you troubleshoot this issue?
    • Answer: I first check the network connectivity between the user’s machine and the SQL Server. Then, I verify the SQL Server instance is running and accepting connections. I also check login permissions and review any error messages in the SQL Server error log and event viewer.
16. You receive an alert that a SQL Server job has failed. What steps do you take to investigate and resolve the issue?
    • Answer: I review the job history to identify the error message and the step that failed. I analyze the error details, check logs, and validate the job configuration. Based on the findings, I correct any issues (e.g., permissions, resource availability) and rerun the job.
17. Describe your process for applying SQL Server patches and updates in a production environment. How do you minimize downtime and ensure a smooth upgrade?
    • Answer: I schedule patching during maintenance windows to minimize impact. I test patches in a staging environment first, ensure backups are taken, and communicate with stakeholders. During patching, I monitor the process and verify the SQL Server instance’s health post-patching.
18. How do you handle a situation where a database is running out of space? What are your immediate and long-term actions?
    • Answer: Immediately, I check for large transactions and growth patterns. I add space by extending the database file or adding new files. Long-term, I archive old data, review and adjust autogrowth settings, and monitor disk space usage regularly to prevent future issues.

Miscellaneous

19. How do you handle version control and deployment of database changes in a team environment?
    • Answer: I use version control systems like Git to manage database scripts. I ensure changes are reviewed and tested in a staging environment before deployment. Automated deployment tools help in consistent and reliable application of changes across environments.
20. Can you describe a time when you had to optimize a SQL Server environment for a high-transaction application? What challenges did you face and how did you address them?
    • Answer: I optimized a high-transaction application by partitioning large tables, optimizing indexes, and ensuring queries were efficient. Challenges included managing locking and blocking, which I addressed by using appropriate isolation levels and optimizing transaction scopes.
21. What tools and scripts do you use for routine database maintenance tasks?
    • Answer: I use SQL Server Maintenance Plans, Ola Hallengren’s maintenance scripts for backups and index maintenance, and custom scripts for monitoring performance and space usage. These tools help automate and standardize routine tasks, ensuring database health and performance.

These answers demonstrate a solid understanding of SQL Server DBA responsibilities and the ability to handle real-world challenges effectively.