Apache Cassandra is a distributed NoSQL database system designed for managing large amounts of structured data across multiple commodity servers. Known for its high availability, fault tolerance, and scalability, Cassandra is a popular choice for cloud-native applications, real-time analytics, and data warehousing solutions.
Intro to Cassandra
Initially developed by Facebook to solve their inbox search problem, Cassandra was open-sourced and later became an Apache Software Foundation project. It is built to handle massive data volumes, distribute them across multiple nodes without any single point of failure, and ensure data is always accessible.
Apache Cassandra stands out for its distributed, peer-to-peer architecture, eliminating single points of failure, unlike traditional master-slave databases. It also uses a wide-column store and offers tunable consistency, making it ideal for large, distributed data sets.
Cassandra Quick Facts
Distributed Architecture: Apache Cassandra operates on a peer-to-peer, distributed architecture, meaning there’s no single point of failure and every node in the cluster has the same role.
Highly Scalable: Cassandra is designed for horizontal scalability, allowing you to add more nodes to the system easily without any downtime, making it ideal for applications that require handling large volumes of data across multiple servers.
High Availability and Fault Tolerance: The database automatically replicates data across multiple nodes and even across data centers, ensuring high availability and fault tolerance.
Tunable Consistency: While it operates under an “eventually consistent” model, Cassandra allows for fine-grained control over consistency levels for both read and write operations, enabling you to tune the system according to your specific use-case requirements.
Wide Column Store: Unlike traditional relational databases, Cassandra employs a wide-column store model. This enables high-speed writes and is especially useful for write-heavy applications, time-series data, and real-time analytics.
Key Features of Cassandra
Distributed Architecture: Cassandra uses a peer-to-peer architecture as opposed to master-slave architectures. Every node in the cluster is identical and capable of handling read and write operations.
High Availability and Fault Tolerance: Cassandra offers automatic data replication, which means that data is stored in multiple locations, ensuring system robustness and availability even if nodes or data centers fail.
Scalability: Designed for horizontal scalability, you can easily add more nodes to a Cassandra cluster without any downtime, thus supporting large-scale deployments effortlessly.
Consistency Tuning: While primarily an “eventually consistent” system, Cassandra allows fine-grained control over the consistency level for read and write operations.
Wide Column Store: Unlike traditional relational databases, Cassandra employs a wide-column store model, making it adept at handling write-heavy workloads and enabling rapid writes.
Cassandra Technical Overview
Cassandra is built on a distributed architecture and uses a ring-like structure where each node communicates with each other. It employs partitioning strategies to distribute data across the cluster and uses various algorithms like consistent hashing for load balancing.
How it Works
Data Distribution: Data is partitioned and distributed across various nodes in the cluster. Each row is identified by a unique key and stored in a sorted order on a node.
Replication: For fault tolerance, data is automatically replicated across multiple nodes. The number of replicas is configurable.
Consistency: Cassandra uses tunable consistency. For any read or write operation, you can specify how many replicas must respond to consider the operation successful.
Read and Write Operations: Cassandra is optimized for high write throughput and can also serve high read throughput if data is denormalized, or if read queries are carefully designed.
Cassandra Versus Alternatives
Cassandra has many different alternatives that could be used instead. It is helpful in understanding Cassandra to compare it to some of its most popular alternatives. The chart below compares Apache Cassandra to Amazon DynamoDB, Google Bigtable, and MongoDB.
Getting Started with Apache Cassandra
Installation
Cassandra runs on a Java Virtual Machine (JVM), so you’ll need to have Java installed. After that, you can download the latest version of Cassandra from its official website.
On Linux or macOS:
# Download and unpack Cassandra
wget http://www.apache.org/dist/cassandra/x.y.z/apache-cassandra-x.y.z-bin.tar.gz
tar -xvf apache-cassandra-x.y.z-bin.tar.gz
# Navigate to the Cassandra directory
cd apache-cassandra-x.y.z
# Start Cassandra
bin/cassandra
Basic Operations with CQL
Cassandra Query Language (CQL) is a SQL-like language for interacting with Cassandra. To enter the CQL shell, type:
bin/cqlsh
Here are some basic CQL commands to get you started:
-- Create a keyspace
CREATE KEYSPACE my_keyspace WITH replication = {'class':'SimpleStrategy', 'replication_factor':1};
-- Use the keyspace
USE my_keyspace;
-- Create a table
CREATE TABLE users(id UUID PRIMARY KEY, name TEXT, age INT);
-- Insert data
INSERT INTO users (id, name, age) VALUES (uuid(), 'Alice', 30);
-- Query data
SELECT * FROM users;
