Apache Cassandra is an open source transactional distributed database written in Java and licensed under Apache-2.0, for users who need linear scalability and proven fault-tolerance on commodity hardware or cloud infrastructure without compromising performance.

What it is

Apache Cassandra is a highly-scalable partitioned row store. Rows are organized into tables with a required primary key, and the database organizes data by rows and columns in a manner similar to relational databases. It lives in the Java ecosystem: Java is required, Python is needed for cqlsh, and the project is listed under Infrastructure & Operations / Databases with the topics cassandra, database, and java. The Cassandra Query Language (CQL) is a close relative of SQL.

The concrete problem Cassandra solves is distribution of rows across multiple machines without forcing the application to manage placement. Partitioning means Cassandra can distribute data across multiple machines in an application-transparent manner, and it will automatically repartition as machines are added to or removed from the cluster. That replaces the application-managed sharding work that would otherwise be required to spread a row store over more than one machine.

Key capabilities

• Partitioned row store: rows are organized into tables with a required primary key, and data can be distributed across multiple machines in an application-transparent manner.
• Automatic repartitioning when machines are added to or removed from the cluster.
• CQL (Cassandra Query Language), a close relative of SQL, with commands such as CREATE KEYSPACE, USE, CREATE TABLE, INSERT, and SELECT.
• bin/cassandra -f starts the server in the foreground and logs to standard out; ctrl-C stops it.
• bin/cqlsh provides an interactive command line client; its banner reports cqlsh 6.3.0, Cassandra 7.0-SNAPSHOT, CQL spec 3.4.8, and Native protocol v5.
• Official Docker image cassandra on Docker Hub, alongside official downloads from the Apache Cassandra web site.
• Apache-2.0 licence, with issues reported on the Apache Jira project CASSANDRA.

Who uses it and how

• Developers evaluating the database stand up a one-node cluster by unpacking apache-cassandra-$VERSION.tar.gz, running bin/cassandra -f, and issuing CQL through bin/cqlsh.
• Operators run clusters across multiple machines on commodity hardware or cloud infrastructure, relying on Cassandra to distribute rows and automatically repartition as machines join or leave.
• Teams building row-store applications that need partitioning to remain application-transparent rather than manually sharded.
• Users who want a CQL interface, close to SQL, for defining keyspaces, tables, and queries.
• Projects that deploy through the official cassandra Docker image or through official Apache Cassandra downloads.

Getting started

Unpack apache-cassandra-$VERSION.tar.gz, then run bin/cassandra -f to start the server in the foreground and bin/cqlsh to open the interactive CQL client. Java must be available, and Python is required for cqlsh.

How it compares

The supplied facts do not name any similar tools or paid products for comparison. On the evidence provided, Apache Cassandra stands alone in this registry.

When to use it — and when not to

A self-hoster must operate the Java runtime and Python for cqlsh, and must run a cluster whose data is partitioned across machines. Cassandra is not a fit for teams that require standard SQL semantics rather than CQL, or that do not want to operate a distributed row store. The README excerpt is sparse and getting-started-focused, and the repository shows 529 open issues, so operators should expect to consult the full documentation and Jira rather than rely on the README alone.