Interview Questions and Answers
Freshers / Beginner level questions & answers
Ques 1. What is Apache Cassandra?
Apache Cassandra is a highly scalable and distributed NoSQL database system designed to handle large amounts of data across multiple commodity servers without a single point of failure.
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Ques 2. What is a key space in Cassandra?
A key space in Cassandra is a namespace that defines data replication on nodes. It is the outermost container for data, similar to a database in the relational database world.
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Ques 3. Explain the concept of a node in Cassandra.
A node in Cassandra is an individual server that stores data. Nodes work together to form a distributed and decentralized database system.
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Ques 4. What is a column family in Cassandra?
In Cassandra, a column family is a container for rows. It is similar to a table in a relational database and consists of columns and rows.
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Ques 5. What is a Cassandra data center?
A Cassandra data center is a logical grouping of nodes that are geographically close to each other. Data centers are used for replication and fault tolerance purposes.
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Ques 6. How does Cassandra ensure fault tolerance?
Cassandra achieves fault tolerance through data replication. Each piece of data is replicated across multiple nodes in the cluster, ensuring that if a node fails, the data is still available on other nodes.
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Ques 7. What is the purpose of the nodetool utility in Cassandra?
Nodetool is a command-line utility in Cassandra that provides various administrative tasks, such as monitoring the cluster, managing compaction, and performing other maintenance operations.
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Ques 8. What is the CQL (Cassandra Query Language)?
CQL is a query language for interacting with Cassandra databases. It is similar to SQL but is specifically designed for NoSQL databases and includes support for creating, updating, and querying data in Cassandra.
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Intermediate / 1 to 5 years experienced level questions & answers
Ques 9. Explain the CAP theorem and how it relates to Cassandra.
The CAP theorem states that a distributed system cannot simultaneously provide more than two out of three guarantees: Consistency, Availability, and Partition Tolerance. Cassandra prioritizes Availability and Partition Tolerance over Consistency, making it an AP system.
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Ques 10. What is a partition key in Cassandra?
A partition key is a primary key assigned to each row in a Cassandra table. It is responsible for distributing data across nodes in the cluster and is crucial for the performance of queries.
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Ques 11. Explain the role of the Snitch in Cassandra.
The Snitch in Cassandra is responsible for determining the proximity of nodes in a cluster. It helps in optimizing data distribution and ensures that data is stored on nodes that are geographically closer to each other.
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Ques 12. Explain the importance of the commit log in Cassandra.
The commit log in Cassandra is crucial for durability and fault tolerance. It stores write operations before they are written to the actual data files, ensuring that data is not lost in the event of a node failure.
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Ques 13. What is a compaction in Cassandra?
Compaction in Cassandra is the process of merging and compacting SSTables (sorted string tables) to optimize storage and improve read performance.
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Ques 14. How does Cassandra handle write operations?
Cassandra uses a write-ahead log (WAL) and a memtable for write operations. Data is first written to the commit log for durability and then stored in the memtable, which is periodically flushed to an SSTable on disk.
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Ques 15. Explain the concept of eventual consistency in Cassandra.
Eventual consistency in Cassandra means that, given enough time and in the absence of further updates, all replicas of a piece of data will converge to the same value. It allows for high availability and partition tolerance but may result in temporarily inconsistent data.
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Ques 16. Explain the role of the Gossip Protocol in Cassandra.
The Gossip Protocol is used by nodes in a Cassandra cluster to communicate with each other and share information about the state of the cluster. It helps in maintaining a decentralized and dynamic view of the cluster.
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Ques 17. How does Cassandra handle read operations?
Cassandra uses a combination of partition key and clustering key to locate and retrieve data efficiently. Read operations can be served from memory (memtable) or disk (SSTables), depending on the specific scenario.
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Ques 18. Explain the difference between a wide row and a narrow row in Cassandra.
A wide row in Cassandra contains a large number of columns, while a narrow row has a smaller number of columns. The distinction is important for designing data models based on query requirements and performance considerations.
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Ques 19. What is the role of a coordinator node in Cassandra?
The coordinator node in Cassandra is responsible for receiving and coordinating client requests. It determines the nodes that need to be involved in the request and communicates with them to fulfill the operation.
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Ques 20. Explain the concept of a quorum in Cassandra.
A quorum in Cassandra is a majority of replicas that must respond for a read or write operation to be considered successful. The quorum level is configurable and is used to ensure consistency in distributed systems.
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Experienced / Expert level questions & answers
Ques 21. What is a secondary index in Cassandra?
A secondary index in Cassandra allows querying on columns other than the primary key. However, the use of secondary indexes should be carefully considered due to potential performance implications.
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Ques 22. How does Cassandra handle data distribution across nodes?
Cassandra uses a consistent hashing algorithm to distribute data across nodes in the cluster. This ensures a uniform distribution of data and facilitates efficient data retrieval.
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Ques 23. What are the different compaction strategies in Cassandra?
Cassandra supports several compaction strategies, including SizeTieredCompactionStrategy, LeveledCompactionStrategy, and TimeWindowCompactionStrategy. Each strategy has its own advantages and is suited for specific use cases.
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Ques 24. Explain the concept of tombstones in Cassandra.
Tombstones in Cassandra are markers used to represent deleted data. They are necessary for eventual consistency and are used during the process of data cleanup and compaction.
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Ques 25. What is a lightweight transaction in Cassandra?
A lightweight transaction in Cassandra is a form of conditional update that ensures atomicity and isolation. It allows for conditional updates based on the current state of the data.
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