Updated June 15, 2023
Introduction to Cassandra Interview Questions
This article consists of Cassandra’s Interview Questions And Answers. Apache Cassandra is a highly available “NoSQL” distributed database management system. It is a type of NoSQL database. Cassandra became a top-level Apache Project in 2010. Cassandra has been written in Java; hence, it can run on various operating systems and platforms. It can be flexible in Real-time storing the data for online applications and reading data for the business intelligence system.
Frequently Asked Cassandra Interview Questions and Answers
You have finally found your dream job in Cassandra but are wondering how to crack the 2023 Cassandra Interview and what could be the probable Cassandra interview questions. Every Cassandra interview is different, and the job scope is different too. Keeping this in mind, we have designed the most common Cassandra Interview Questions and Answers to help you get success in your interview.
Part 1 – Cassandra Interview Questions (Basics)
This first part covers the basic Interview Questions.
1. What is NoSQL? How many types of NoSQL databases are there?
Answer:
NoSQL (sometimes expanded to “not only SQL “) could be a broad category of management systems that dissent from the classic model of the relational database management system (RDBMS) in some significant ways.
NoSQL systems:
– Specifically designed for top load
– Natively supports horizontal scalability
– Do not usually store data in a table
– Sometimes offer ultimate consistency rather than ACID transactions
– Fault-tolerant
– Store data in the demoralized manner
In contrast to RDBMS, NoSQL systems:
- Usually not offer support for distributed transactions
- Do not guarantee data consistency
- Do not sometimes use some advanced ideas of RDBMS, like triggers, views, hold-on procedures.
NoSQL implementations can be categorized by their manner of performance:
- Document Stores (MongoDB, Couchbase)
- Key-Value Stores (Redis, Voldemort)
- Column Stores (Cassandra)
- Graph Stores (Neo4j, Giraph)
- Multivalued databases
- Object databases
- Triplestore
- Tuple store
2. Explain what Cassandra is. Why is Cassandra preferred over different NoSQL databases like HBase?
Answer:
Facebook developed Apache Cassandra as a highly available “NoSQL” distributed database management system. It is open source and designed to handle large amounts of data, offering high availability without a single point of failure. In 2010, Cassandra became a top-level Apache project after Facebook open-sourced the code. It is a type of NoSQL database. It can serve as both.
- Real-time data storage system for online applications
- Also, read data for the business intelligence system
Cassandra is designed for large-scale distributed data to optimize performance and availability, with a particular emphasis on very fast writes.
The various factors responsible for using Cassandra are
- Gigabytes to petabytes scalabilities
- It could be a column-oriented information
- No single purpose for failure
- No want for a separate caching layer
- Flexible schema style
- It has versatile data storage, simple knowledge distribution, and quick writes.
- It supports ACID (Atomicity, Consistency, Isolation, and Durability) properties.
- Multi-datacentre and cloud-capable
- Data compression
3. What is SSTable?
Answer:
SSTable, also known as the ‘Sorted String Table,’ is a data structure Cassandra uses to store data on a disk. Being changeless, SStables don’t enable to any extent, further addition and removal of data items once written. For every SSTable, 3 files are created by Cassandra, like partition index, partition outline, and a bloom filter.
4. Define Mem-table in Cassandra.
Answer:
It is a memory-resident data structure. Once the commit log, the info is written to the mem-table. Mem-table is an in-memory/write-back cache house consisting of the content in key and column format.
5. How Cassandra stores data?
Answer:
- When you specify a validator, Cassandra ensures those bytes square measure encoded as per demand.
- While composite stores a two-byte length for every element followed by the computer memory unit encoded part and a termination bit, it is essentially just byte arrays with a specific encoding.
Part 2 – Cassandra Interview Questions (Advanced)
Let us now have a look at the advanced Interview Questions.
1. Mention what Cassandra- CQL collections is.
Answer:
Cassandra provides a prompt Cassandra query language shell (cqlsh) using which you can execute Cassandra Query Language (CQL). In Cassandra, you can use CQL collections in the following ways.
- List: it’s used once the order of the info has to be maintained, and worth is to be held on multiple times (contains the list of distinctive elements)
- SET: it’s used for the cluster of components to store and come back in sorted orders
- MAP: It is a data type used to store a key-value pair of elements
2. Explain the Cassandra Data Model.
Answer:
The Cassandra data model consists of 4 main pillars: the cluster, keyspace, column, column & family.
- Clusters: Clusters contain many nodes (machines) and can contain multiple vital spaces.
- Keyspace: A keyspace is a namespace to group multiple column families.
- Column: A column has a name, value, and timestamp.
- Family: A column family contains multiple columns referenced by a row of keys.
3. Explain how Cassandra writes.
Answer:
Cassandra first writes data to a commit log and then associates it in a memorable and in the table. A write is successful when both commits are complete. In the event of a fault, once writing to the SSTable, Cassandra will merely replay the commit log.
4. Explain how Cassandra deletes Data.
Answer:
SSTables are changeless tables. Once a row has to be deleted, Cassandra assigns the column value with a particular value referred to as Tombstone.
5. What is tunable Consistency in Cassandra? How many types of tunable Consistency are supported in Cassandra?
Answer:
Tunable Consistency could be a fantastic characteristic of Cassandra that makes it a preferred selection. Consistency refers to the up-to-date and synchronous data rows on all their replicas. Cassandra’s Tunable Cassandra’s Tunable Consistency allows users to pick the consistency most suited to their use cases.
It supports two consistencies: Eventual Consistency and Strong Consistency.
Eventual Consistency: Once a given data item has no new updates, the system employs eventual consistency, where all accesses eventually return the last updated value.
Cassandra’s subsequent conditions for robust Consistency:
R + W > N
Here
N: Number of replicas
W: Number of nodes that need to agree for a successful write
R: Number of nodes that need to agree for a successful read
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