Cassandra Interview Questions and Answers for internship

1. What is Cassandra?

   • Answer: Cassandra is a highly scalable, distributed, NoSQL database management system designed to handle large amounts of data across many commodity servers, providing high availability with no single point of failure.

2. What are the key features of Cassandra?

   • Answer: Key features include high availability, scalability, fault tolerance, linear scalability, and flexible schema.

3. Explain the concept of a distributed database.

   • Answer: A distributed database is a database in which data is stored across multiple computers, connected through a network. This allows for increased scalability and availability.

4. What is a consistency level in Cassandra?

   • Answer: Consistency levels define how many replicas must acknowledge a write operation before it's considered successful. Options include ONE, TWO, THREE, QUORUM, ALL, LOCAL_QUORUM, EACH_QUORUM.

5. Explain the difference between consistency and availability.

   • Answer: Consistency ensures that all nodes see the same data at the same time, while availability prioritizes ensuring that the system remains operational even if some nodes are down. There's a trade-off between the two, known as the CAP theorem.

6. What is the CAP theorem?

   • Answer: The CAP theorem states that a distributed data store can provide only two out of the following three guarantees: Consistency, Availability, and Partition tolerance. Cassandra prioritizes Availability and Partition tolerance.

7. What is a data model in Cassandra?

   • Answer: Cassandra uses a wide-column store data model. Data is organized into keyspaces, tables (column families), rows, and columns. Each row is identified by a primary key.

8. Explain the concept of a keyspace in Cassandra.

   • Answer: A keyspace is a top-level container for tables in Cassandra. It's analogous to a database in relational databases.

9. What is a column family in Cassandra?

   • Answer: A column family is a table in Cassandra. It's a collection of rows that share the same structure and properties.

10. What is a primary key in Cassandra?

    • Answer: The primary key uniquely identifies a row in a Cassandra table. It can be composed of a partition key and a clustering key.

11. Explain the difference between a partition key and a clustering key.

    • Answer: The partition key determines how data is distributed across nodes. The clustering key orders the data within each partition.

12. What is data modeling in Cassandra?

    • Answer: Data modeling in Cassandra involves designing the keyspace, tables, and primary keys to optimize query performance and data distribution.

13. How does Cassandra handle data replication?

    • Answer: Cassandra replicates data across multiple nodes to ensure high availability and fault tolerance. The replication factor determines the number of replicas for each data partition.

14. What is a replication factor?

    • Answer: The replication factor specifies the number of replicas for each partition of data in Cassandra. A higher replication factor increases fault tolerance but reduces write performance.

15. What is read repair in Cassandra?

    • Answer: Read repair is a process where Cassandra automatically corrects inconsistencies between replicas when reading data. It ensures data consistency across replicas.

16. What is hinted handoff in Cassandra?

    • Answer: Hinted handoff is a mechanism Cassandra uses to handle write failures. When a node is down, Cassandra stores the write in a temporary location (hint) and delivers it when the node recovers.

17. How does Cassandra handle data consistency?

    • Answer: Cassandra uses consistency levels to control how many replicas must acknowledge a write operation before it's considered successful. It also uses read repair and anti-entropy processes to maintain data consistency.

18. Explain the concept of gossip protocol in Cassandra.

    • Answer: The gossip protocol is a peer-to-peer communication mechanism used by Cassandra nodes to maintain cluster membership information, monitor node health, and perform other cluster management tasks.

19. What is a tombstone in Cassandra?

    • Answer: A tombstone is a marker indicating that a column or row has been deleted. It's eventually removed during garbage collection.

20. What is compaction in Cassandra?

    • Answer: Compaction is a process where Cassandra merges multiple smaller SSTables (Sorted Strings Tables) into larger ones to improve read performance and reduce storage space.

21. What are SSTables in Cassandra?

    • Answer: SSTables (Sorted Strings Tables) are immutable files that store Cassandra data on disk. They are sorted by row key and are crucial for efficient data retrieval.

22. How does Cassandra handle schema changes?

    • Answer: Cassandra uses a schema-on-write approach, meaning schema changes are applied automatically during write operations without requiring downtime. Backward compatibility is maintained.

23. What are some common Cassandra use cases?

    • Answer: Common use cases include handling large volumes of log data, time series data, and real-time analytics applications. It's also used for handling high-volume writes and providing high availability services.

24. What are some advantages of using Cassandra?

    • Answer: Advantages include high scalability, high availability, fault tolerance, excellent performance for high-volume writes, and flexible schema.

25. What are some disadvantages of using Cassandra?

    • Answer: Disadvantages include complex data modeling, limited support for complex joins, and potential challenges in managing large clusters.

26. How would you choose between Cassandra and a relational database?

    • Answer: The choice depends on the specific application requirements. Cassandra is ideal for high-volume write scenarios, large datasets, and applications where high availability and scalability are paramount. Relational databases are better suited for applications requiring complex joins, ACID properties, and strong consistency.

27. What is CQL?

    • Answer: CQL (Cassandra Query Language) is the query language used to interact with Cassandra databases. It's similar to SQL but tailored to Cassandra's data model.

28. Write a CQL query to create a keyspace.

    • Answer: CREATE KEYSPACE my_keyspace WITH replication = {'class': 'SimpleStrategy', 'replication_factor': '3'};

29. Write a CQL query to create a table.

    • Answer: CREATE TABLE my_table (id uuid PRIMARY KEY, name text, age int);

30. Write a CQL query to insert data into a table.

    • Answer: INSERT INTO my_table (id, name, age) VALUES (uuid(), 'John Doe', 30);

31. Write a CQL query to select data from a table.

    • Answer: SELECT * FROM my_table;

32. Write a CQL query to update data in a table.

    • Answer: UPDATE my_table SET age = 31 WHERE id = uuid();

33. Write a CQL query to delete data from a table.

    • Answer: DELETE FROM my_table WHERE id = uuid();

34. Explain different data types in Cassandra.

    • Answer: Cassandra supports various data types including ascii, bigint, blob, boolean, counter, date, decimal, double, float, inet, int, list, map, set, text, timestamp, timeuuid, tinyint, uuid, varchar.

35. What is the use of counter data type?

    • Answer: The counter data type is used for atomically incrementing or decrementing values. It's useful for tracking counts or metrics.

36. What are some common Cassandra performance tuning techniques?

    • Answer: Techniques include proper data modeling, choosing appropriate consistency levels, optimizing read/write patterns, using appropriate compaction strategies, and monitoring cluster performance.

37. How do you monitor a Cassandra cluster?

    • Answer: Tools like Nodetool, JMX, and various monitoring systems (like Prometheus, Grafana) can be used to monitor various aspects of the cluster health, resource utilization, and performance metrics.

38. What is the role of Cassandra in a microservices architecture?

    • Answer: Cassandra can serve as a highly scalable and available database for various microservices, handling their individual data storage needs independently.

39. How does Cassandra handle failures?

    • Answer: Cassandra handles failures through replication, hinted handoff, and automatic failover. It can continue operating even if some nodes are down.

40. What is the difference between Cassandra and DynamoDB?

    • Answer: Both are NoSQL databases, but DynamoDB is a managed service offered by AWS, while Cassandra is an open-source database. DynamoDB offers simpler management, while Cassandra provides more control and flexibility.

41. How would you troubleshoot a slow query in Cassandra?

    • Answer: Troubleshooting involves examining query execution plans, checking for hotspots in the data model, ensuring proper indexing, and monitoring resource usage. Tools like Nodetool can be helpful.

42. Describe your experience with NoSQL databases.

    • Answer: [This answer should be tailored to your experience. Mention specific NoSQL databases used, projects worked on, and skills acquired.]

43. What are your strengths and weaknesses?

    • Answer: [This answer should be tailored to your individual strengths and weaknesses. Focus on relevant technical skills and areas for improvement.]

44. Why are you interested in this internship?

    • Answer: [This answer should be tailored to your interest in the specific internship and company.]

45. What are your salary expectations?

    • Answer: [This answer should be tailored to your research on typical internship salaries in your area.]

46. Tell me about a time you faced a challenging technical problem. How did you solve it?

    • Answer: [This answer should describe a specific technical challenge and detail the steps taken to solve it. Highlight problem-solving skills and technical abilities.]

47. Tell me about a time you worked effectively as part of a team.

    • Answer: [This answer should illustrate teamwork skills and collaborative experiences.]

48. How do you stay updated with the latest technologies?

    • Answer: [Mention specific methods like reading technical blogs, attending conferences, taking online courses, etc.]

49. What are your career goals?

    • Answer: [Clearly articulate your career aspirations and how this internship fits into your plan.]

50. Do you have any questions for me?

    • Answer: [Prepare insightful questions about the internship, team, projects, and company culture.]

51. Explain your understanding of distributed systems.

    • Answer: [Discuss concepts like fault tolerance, consistency, availability, and scalability in distributed systems.]

52. What is your experience with Git and version control?

    • Answer: [Describe your proficiency with Git commands, branching strategies, and collaborative workflows.]

53. What is your experience with any cloud platforms (AWS, Azure, GCP)?

    • Answer: [Describe any experience with cloud platforms, including services used and tasks performed.]

54. What is your experience with Linux or other operating systems?

    • Answer: [Describe your comfort level with command-line interfaces and system administration tasks.]

55. Describe your experience with data structures and algorithms.

    • Answer: [Discuss your knowledge of common data structures like arrays, linked lists, trees, graphs, and algorithms like sorting and searching.]

56. What is your preferred programming language and why?

    • Answer: [Justify your choice based on relevant experience and suitability for the role.]

57. How do you handle stress and pressure?

    • Answer: [Describe healthy coping mechanisms and strategies for managing workload.]

58. Describe your problem-solving approach.

    • Answer: [Explain your systematic approach to problem-solving, including steps like defining the problem, gathering information, developing solutions, and testing them.]

59. How do you learn new technologies quickly?

    • Answer: [Describe your learning style and preferred methods for acquiring new skills.]

60. What is your understanding of the software development lifecycle (SDLC)?

    • Answer: [Explain your knowledge of different SDLC methodologies like Agile, Waterfall, etc.]

61. What are your expectations from this internship?

    • Answer: [Clearly articulate your learning objectives and contributions to the team.]

62. How would you contribute to our team?

    • Answer: [Highlight your skills and experiences that align with the team's needs and goals.]

63. Are you comfortable working in a fast-paced environment?

    • Answer: [Answer affirmatively and provide examples of handling pressure and meeting deadlines.]

64. How do you handle feedback?

    • Answer: [Express your willingness to receive constructive criticism and use it to improve your skills.]

65. What is your availability for the internship?

    • Answer: [State your availability clearly and honestly.]

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