Top 20 Apache Cassandra Interview Questions and Answers

10/15/2025

Apache Cassandra Interview Questions and Answers 2025

Go Back

Top 20 Apache Cassandra Interview Questions and Answers (2025 Guide)

Introduction

Apache Cassandra is one of the most powerful NoSQL distributed databases designed to handle massive volumes of data with high availability, fault tolerance, and scalability. It is widely used in data-driven industries for handling big data, analytics, and real-time processing.

If you’re preparing for a Cassandra interview in 2025, this comprehensive guide will help you master the top 20 Apache Cassandra interview questions and answers to boost your confidence and skills.

1. What is Apache Cassandra?

Answer:
Apache Cassandra is an open-source, distributed NoSQL database that manages large amounts of structured, semi-structured, and unstructured data. It provides linear scalability, decentralized architecture, and no single point of failure.

2. What are the key features of Cassandra?

Answer:

  • Decentralized peer-to-peer architecture

  • Fault-tolerant and scalable design

  • Tunable consistency

  • High availability and durability

  • Flexible schema

  • Cross-data center replication

3. Explain the architecture of Cassandra.

Answer:
Cassandra’s architecture is ring-based and uses a peer-to-peer network where every node is equal. Data is distributed using consistent hashing, and communication between nodes happens via the Gossip protocol.

4. What is a Keyspace in Cassandra?

Answer:
A Keyspace is the top-level namespace in Cassandra, similar to a database in RDBMS. It defines replication factors and data replication strategies.

Example:

 
CREATE KEYSPACE ecommerce WITH replication = {'class': 'SimpleStrategy', 'replication_factor' : 3};
5. What is a Column Family?
Answer:
A Column Family is a collection of rows identified by a unique key, much like a table in traditional databases.
6. What is a Node in Cassandra?
Answer:
A Node is the basic unit of data storage in Cassandra. Each node contains part of the overall dataset and communicates with others to maintain cluster integrity.
7. What is a Cluster?
Answer:
A Cluster is a collection of interconnected Cassandra nodes that store and replicate data across the system for high availability.
8. Explain Data Replication in Cassandra.
Answer:
Cassandra replicates data across multiple nodes to ensure fault tolerance and data durability.
  • Replication Factor → Number of data copies.
  • Replication Strategy → Can be SimpleStrategy or NetworkTopologyStrategy.
9. What is Consistency Level in Cassandra?
Answer:
The Consistency Level defines how many replicas must acknowledge a read or write operation before it’s considered successful.
Examples:
  • ONE
  • QUORUM
  • ALL
10. What is the Gossip Protocol?
Answer:
The Gossip protocol is a peer-to-peer mechanism used by Cassandra to share information about node states and detect failures.
11. What is a Partition Key?
Answer:
The Partition Key determines the distribution of data across nodes. It’s part of the Primary Key and ensures even data partitioning.
12. What is a Commit Log in Cassandra?
Answer:
A Commit Log records all write operations for crash recovery. Each write is first stored in the commit log before being written to memory.
13. What are SSTables?
Answer:
SSTables (Sorted String Tables) are immutable disk files that store data flushed from MemTables.
14. What is a MemTable?
Answer:
A MemTable is an in-memory data structure that temporarily holds write operations before being flushed to disk.
15. Explain the Write Path in Cassandra.
Answer:
  1. Write → Commit Log
  2. Data → MemTable
  3. MemTable → SSTable (when full)
  4. Compaction merges SSTables periodically
16. Explain the Read Path in Cassandra.
Answer:
When reading data, Cassandra checks:
  1. MemTable (recent writes)
  2. Row Cache
  3. Bloom Filter → To find data in SSTables
17. What is a Bloom Filter?
Answer:
A Bloom Filter is a space-efficient probabilistic data structure that helps Cassandra quickly determine if data may exist in an SSTable, reducing unnecessary disk reads.
18. How does Cassandra handle node failures?
Answer:
Cassandra ensures fault tolerance through:
  • Replication of data across nodes.
  • Hinted Handoff → Stores writes temporarily for failed nodes.
  • Read Repair and Anti-Entropy Repair to maintain consistency.
19. What is Compaction in Cassandra?
Answer:
Compaction merges multiple SSTables into a single table, removing obsolete or deleted data and improving read efficiency.
20. How do you optimize Cassandra performance?
Answer:
  • Tune parameters in cassandra.yaml.
  • Use appropriate partition keys.
  • Monitor performance with nodetool.
  • Choose optimal compaction strategies.
  • Scale horizontally by adding nodes.
 
Conclusion
Apache Cassandra continues to be a leading choice for distributed database solutions in 2025. Understanding its architecture, replication strategies, and optimization techniques will help you excel in your interviews and real-world implementations.
 
 Apache Cassandra Interview Questions and Answers 2025
Table of content