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 is open-source and is designed in such a way that it can handle large amounts of data, providing high availability that has no single point of failure. Cassandra became a top-level Apache Project in 2010. Cassandra has been written in Java; hence, it can run on a vast array of operating systems and platforms. It can be flexible in Real-time storing the data for online applications as well as it can read 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:
Apache Cassandra is a highly available “NoSQL” distributed database management system that is open source and designed to handle large amounts of data, providing high availability with no single point of failure. Cassandra was developed at Facebook, and after Facebook open-sourced the code, Cassandra became a top-level Apache project in 2010. It is a type of NoSQL database. Cassandra is written in Java and can run on various operating systems and platforms. It can serve as both.
- Real-time data storage system for online applications
- Also, read data for the business intelligence system
For performance and availability, Cassandra is designed for large-scale distributed data, and it is optimized for 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 is also known as the ‘Sorted String Table.’ In it, memorable are stored on disk and exist for each Cassandra table. 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. The information in mem- a table is sorted by key, and every column family consists of a definite mem-table that retrieves column knowledge via the key.
5. How Cassandra stores data?
Answer:
- All data is held on as bytes.
- When you specify a validator, Cassandra ensures those bytes square measure encoded as per demand.
- While composite is just byte arrays with a specific encoding, it stores a two-byte length for every element followed by the computer memory unit encoded part and a termination bit.
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 table. A write is successful when both commits are complete. Memtables and SSTables are created per column family. Writes are written to disk in a table structure called an SSTable (sorted string table). In the event of a fault, once writing to the SSTable, Cassandra will merely replay the commit log. With this style, Cassandra has the lowest disk I/O and offers high-speed write performance due to the commit log being append-only, and Cassandra doesn’t look for on-writes.
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. Once the data is read, the Tombstone value is taken into account as deleted.
- 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: The eventual Consistency is employed once no new updates are made on a given data item; all accesses return the last updated worth eventually—systems with eventual Consistency famed to own achieved reproduction convergence.
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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