db2 dba Interview Questions and Answers

1. What is DB2?

   • Answer: DB2 (Database 2) is a relational database management system (RDBMS) developed and marketed by IBM. It's known for its scalability, reliability, and performance, often used in enterprise-level applications and data warehousing.

2. Explain the different DB2 editions.

   • Answer: DB2 offers various editions tailored to different needs, including DB2 Enterprise Server Edition (for large-scale deployments), DB2 Express-C (free edition for developers and small deployments), DB2 for Linux, UNIX, and Windows, and DB2 for z/OS (mainframe environment). Each edition offers varying features and licensing.

3. What are tablespaces in DB2?

   • Answer: Tablespaces are logical containers for data within a DB2 database. They group related data objects together and can be managed independently, allowing for better organization and performance tuning. Different tablespaces can have different storage characteristics.

4. Describe the different types of tablespaces.

   • Answer: Common types include simple tablespaces (single contiguous space), segmented tablespaces (divided into segments for better space management), and partitioned tablespaces (distributed across multiple disks for high availability and scalability).

5. Explain indexes in DB2.

   • Answer: Indexes are data structures that improve the speed of data retrieval in DB2. They create a pointer to the actual data rows, allowing for faster lookups based on specific columns. Different index types exist, such as B-tree indexes (most common), unique indexes (ensure uniqueness of values), and others.

6. What is a buffer pool in DB2?

   • Answer: A buffer pool is a memory area in DB2 that caches frequently accessed data pages. This significantly speeds up data access by minimizing disk I/O. DB2 automatically manages buffer pool size, but it can be tuned for optimal performance.

7. How do you monitor DB2 performance?

   • Answer: DB2 performance monitoring involves using system monitoring tools like the DB2 Performance Monitor, analyzing system logs, and using performance views to track metrics like CPU usage, I/O wait times, buffer pool activity, and lock contention. Tools like SQL Performance Analyzer can also be valuable.

8. What are the different types of DB2 locks?

   • Answer: DB2 uses various locking mechanisms to ensure data integrity and concurrency. These include shared locks (allow multiple reads), exclusive locks (prevent concurrent modifications), and update locks (hold a row for exclusive access after reading).

9. Explain deadlocks in DB2.

   • Answer: Deadlocks occur when two or more transactions are blocked indefinitely, waiting for each other to release locks. DB2's deadlock detection mechanism identifies and resolves deadlocks by rolling back one of the involved transactions.

10. How do you troubleshoot deadlocks in DB2?

    • Answer: Troubleshooting deadlocks involves analyzing DB2 logs, identifying the involved transactions and the locks they are holding, and possibly optimizing application code or database design to reduce lock contention. Analyzing wait times and lock statistics can be helpful.

11. What is a stored procedure in DB2?

    • Answer: A stored procedure is a pre-compiled SQL code block stored in the database. It improves performance and code reusability. It can accept parameters, perform complex operations, and return results.

12. What are triggers in DB2?

    • Answer: Triggers are stored procedures automatically executed in response to specific events on a table, such as INSERT, UPDATE, or DELETE operations. They are useful for enforcing data integrity rules or performing actions based on data modifications.

13. Explain the concept of referential integrity.

    • Answer: Referential integrity ensures that relationships between tables are consistent. It prevents actions that would destroy links between related data. For example, it prevents deleting a record in a parent table if there are corresponding records in a child table.

14. What are foreign keys?

    • Answer: Foreign keys are columns in one table that refer to the primary key of another table. They enforce referential integrity by ensuring that values in the foreign key column match existing values in the referenced primary key column.

15. How do you backup and restore a DB2 database?

    • Answer: DB2 provides utilities for backing up and restoring databases. Methods include full backups (entire database), incremental backups (changes since the last backup), and online backups (performed without taking the database offline). The `db2 backup` and `db2 restore` commands are key.

16. What are different backup strategies for DB2?

    • Answer: Backup strategies vary depending on recovery time objectives (RTO) and recovery point objectives (RPO). Strategies include full backup with incremental backups, or a combination of full and differential backups. The choice depends on the frequency of data changes and acceptable downtime.

17. Explain the concept of high availability in DB2.

    • Answer: High availability refers to minimizing downtime and ensuring continued database access even during failures. Techniques include using techniques like clustering (multiple instances working together), and mirroring (copying the database to a standby server).

18. What is DB2 pureScale?

    • Answer: DB2 pureScale is a high-availability and scalability feature that allows for the creation of a cluster of database servers to manage a single database. It enables automatic failover and load balancing across multiple instances.

19. Explain the use of DB2 catalog tables.

    • Answer: DB2 catalog tables store metadata about the database, such as table definitions, index information, and user privileges. They are used by DB2 internally and can be queried by DBAs to gather information about the database structure and objects.

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