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Cassandra Interview Questions and Answers

1
Explain what is Cassandra?

Cassandra is an open source data storage system developed at Facebook for inbox search and designed for storing and managing large amounts of data across commodity servers. It can server as both

Real time data store system for online applications
Also as a read intensive database for business intelligence system

2
List the benefits of using Cassandra.

Unlike traditional or any other database, Apache Cassandradelivers near real-time performance simplifying the work of Developers, Administrators, Data Analysts and Software Engineers.

  • Instead of master-slave architecture, Cassandra is established on peer-to-peer architecture ensuring no failure.
  • It also assures phenomenal flexibility as it allows insertion of multiple nodes to any Cassandra cluster in any datacenter. Further, any client can forward its request to any server.
  • Cassandra facilitates extensible scalability and can be easily scaled up and scaled down as per the requirements. With a high throughput for read and write operations, this NoSQL application need not be restarted while scaling.
  • Cassandra is also revered for its strong data replication capability as it allows data storage at multiple locations enabling users to retrieve data from another location if one node fails. Users have the option to set up the number of replicas they want to create.
  • Shows brilliant performance when used for massive datasets and thus, the most preferable NoSQL DB by most organizations.
  • Operates on column-oriented structure and thus, quickens and simplifies the process of slicing. Even data access and retrieval becomes more efficient with column-based data model.
  • Further, Apache Cassandra supports schema-free/schema-optional data model, which un-necessitate the purpose of showing all the columns required by your application.
3
What is the use of Cassandra and why to use Cassandra?

Cassandra was designed to handle big data workloads across multiple nodes without any single point of failure. The various factors responsible for using Cassandra are

  • It is fault tolerant and consistent
  • Gigabytes to petabytes scalabilities
  • It is a column-oriented database
  • No single point of failure
  • No need for separate caching layer
  • Flexible schema design
  • It has flexible data storage, easy data distribution, and fast writes
  • It supports ACID (Atomicity, Consistency, Isolation, and Durability)properties
  • Multi-data center and cloud capable
  • Data compression
4
Explain the concept of Tunable Consistency in Cassandra.

Tunable Consistency is a phenomenal characteristic that makes Cassandra a favored database choice of Developers, Analysts and Big data Architects. Consistency refers to the up-to-date and synchronized data rows on all their replicas. Cassandra’s Tunable Consistency allows users to select the consistency level best suited for their use cases. It supports two consistencies -Eventual and Consistency and Strong Consistency.
The former guarantees consistency when no new updates are made on a given data item, all accesses return the last updated value eventually. Systems with eventual consistency are known to have achieved replica convergence.
For Strong consistency, Cassandra supports the following condition:
R + W > N, where

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

5
Explain what is composite type in Cassandra?

In Cassandra, composite type allows to define key or a column name with a concatenation of data of different type. You can use two types of Composite Type

  • Row Key
  • Column Name
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