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Apache Cassandra

NoSQL Database

Apache Cassandra is a highly scalable distributed NoSQL database that provides high availability and fault tolerance with its masterless architecture, making it a preferred choice for big data applications.

5 minutes 5 Questions

Apache Cassandra is a highly scalable, distributed NoSQL database management system designed to handle large amounts of data across many commodity servers, providing high availability with no single point of failure. Originally developed at Facebook to power their inbox search feature, Cassandra was released as an open-source project in 2008 and later became a top-level Apache project. Cassandra's architecture is based on a ring topology where data is distributed among all nodes in the cluster. It implements a masterless, peer-to-peer design where all nodes are equal, eliminating bottlenecks and ensuring fault tolerance. The system uses consistent hashing to distribute data across the cluster and supports tunable consistency levels, allowing developers to balance between data consistency and availability according to application requirements. Key features of Cassandra include: 1. Linear scalability - Performance increases linearly as new machines are added 2. Decentralized - No single point of failure with symmetric nodes 3. Tunable consistency - Flexible trade-offs between consistency and availability 4. Flexible data model - Support for both structured and unstructured data 5. High write throughput - Optimized for write-heavy workloads 6. Geographic distribution - Multi-datacenter replication for global deployments Cassandra uses its own query language called CQL (Cassandra Query Language), which resembles SQL but is adapted for its data model. The data model consists of keyspaces (similar to databases), tables, and rows organized in a column-family structure. In Big Data ecosystems, Cassandra often serves as the operational database that handles real-time data needs, complementing analytical systems like Hadoop. It's particularly well-suited for time-series data, product catalogs, messaging platforms, and IoT applications requiring high throughput and low latency at scale. Companies like Netflix, Apple, Instagram, and Spotify rely on Cassandra to manage their massive data workloads.

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Big Data Engineer - Apache Cassandra Example Questions

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Question 1

What is a Write Ahead Log (WAL) in Apache Cassandra?

A data structure used to store recently written data in memory. A type of node in a cluster that is responsible for handling reads and writes. A tool used to replicate data between Cassandra clusters. A file format used to store Cassandra data on disk. A log file used to store data modifications before they are written to disk. A tool used to optimize data queries in Cassandra.

Correct Answer: A log file used to store data modifications before they are written to disk.

The Write Ahead Log (WAL) is a log file that records every write operation before it is written to disk as an SSTable. It is used as a safety mechanism to ensure that no data is lost in case of a crash or power outage. When Cassandra starts up, it reads the WAL to recover any writes that may not be persisted to disk. The WAL is stored on disk and is periodically flushed to disk to minimize the risk of data loss.

Question 2

What is a token in Apache Cassandra?

A value used to monitor the health of the Cassandra cluster A value used to store and retrieve data in Cassandra A value used to optimize query performance A value used to encrypt data at rest in Cassandra A value that defines the position of a node in the ring A value used to replicate data across multiple data centers

Correct Answer: A value that defines the position of a node in the ring

A token is a value calculated from the hash of a node's IP address, and is used to define the position of the node in the Cassandra ring, which determines how data is partitioned, replicated and distributed.

Question 3

What is a partition key in Apache Cassandra?

A type of index used to directly access a specific record in a partition A feature used to secure the partitions using encrypted keys An obsolete feature that was used to limit the size of partitions The node responsible for maintaining a copy of a partition's data A type of column that stores the names of the available partitions The column or set of columns that determines the partition where the data is stored

Correct Answer: The column or set of columns that determines the partition where the data is stored

The partition key determines which node in the cluster will be responsible for storing the corresponding data, so it is a fundamental concept in Apache Cassandra's data model.

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