Apache Cassandra

This article has multiple issues. Please help improve it or discuss these issues on the talk page. (Learn how and when to remove these messages) This article reads like a press release or a news article and may be largely based on routine coverage. Please help improve this article and add independent sources. (October 2023) This article's use of external links may not follow Wikipedia's policies or guidelines. Please improve this article by removing excessive or inappropriate external links, and converting useful links where appropriate into footnote references. (October 2023) (Learn how and when to remove this message) This article contains wording that promotes the subject in a subjective manner without imparting real information. Please remove or replace such wording and instead of making proclamations about a subject's importance, use facts and attribution to demonstrate that importance. (October 2023) (Learn how and when to remove this message) (Learn how and when to remove this message)

Apache Cassandra

Original author(s)	Avinash Lakshman, Prashant Malik / Facebook
Developer(s)	Apache Software Foundation
Initial release	July 2008; 16 years ago (2008-07)
Stable release	5.0.2[1]  / October 19, 2024; 19 days ago (October 19, 2024)
Repository	gitbox.apache.org/repos/asf/cassandra.git
Written in	Java
Operating system	Cross-platform
Available in	English
Type	NoSQL Database, data store
License	Apache License 2.0
Website	cassandra.apache.org

Apache Cassandra is a free and open-source database management system designed to handle large volumes of data across multiple commodity servers. Cassandra supports clusters and spanning of multiple data centers,^[2] featuring asynchronous and masterless replication. It enables low-latency operations for all clients and incorporates Amazon's Dynamo distributed storage and replication techniques, combined with Google's Bigtable data storage engine model.^[3]

Avinash Lakshman, a co-author of Amazon's Dynamo, and Prashant Malik developed Cassandra at Facebook to support the inbox search functionality. Facebook open-sourced Cassandra on Google Code in July 2008,^[4] and it became an Apache Incubator project^[5] in March 2009 and on February 17, 2010, it graduated to a top-level project.^[6]

The developers at Facebook named their database after Cassandra, the Trojan prophetess from mythology, alluding to the classical curse placed on an oracle.^[7]

Apache Cassandra ensures high availability and fault tolerance by allowing every node to perform the same role, thereby eliminating single points of failure. Data is distributed across the cluster using configurable replication strategies that support deployment across multiple data centers, providing redundancy and disaster recovery. The system scales linearly, increasing read and write throughput as new nodes are added, all while maintaining uninterrupted service. Cassandra is classified as an AP (Availability and Partition Tolerance) system, prioritizing availability and partition tolerance over consistency. It offers tunable consistency levels for both reads and writes. Additionally, Cassandra integrates with Hadoop, supporting MapReduce, Apache Pig, and Apache Hive, and features the Cassandra Query Language (CQL) for simplified data access. Eventual consistency is managed through tombstones for reads, upserts, and deletes.

Cassandra introduced the Cassandra Query Language (CQL). CQL is a simple interface for accessing Cassandra, as an alternative to the traditional Structured Query Language (SQL). CQL adds an abstraction layer that hides implementation details of this structure and provides native syntaxes for collections and other common encodings. Language drivers are available for Java (JDBC), Python (DBAPI2), Node.JS (Datastax), Go (gocql) and C++.^[8]

The keyspace in Cassandra is a namespace that defines data replication across nodes. Therefore, replication is defined at the keyspace level. Below is an example of keyspace creation, including a column family in CQL 3.0:^[9]

CREATE KEYSPACE MyKeySpace   WITH REPLICATION = { 'class' : 'SimpleStrategy', 'replication_factor' : 3 };  USE MyKeySpace;  CREATE COLUMNFAMILY MyColumns (id text, lastName text, firstName text, PRIMARY KEY(id));  INSERT INTO MyColumns (id, lastName, firstName) VALUES ('1', 'Doe', 'John');  SELECT * FROM MyColumns; 

Which gives:

 id | lastName | firstName ----+----------+----------   1 | Doe      | John  (1 rows) 

Up to Cassandra 1.0, Cassandra was not row-level consistent, meaning that inserts and updates into the table that affect the same row, and that are processed at approximately the same time, may affect the non-key columns in inconsistent ways.^[10] One update may affect one column while another affects the other, resulting in sets of values within the row that were never specified or intended. Cassandra 1.1 solved this issue by introducing row-level isolation.^[11]

Cassandra is not supported on Windows as of version 4, see issue CASSANDRA-16171.^[12]

Deletion markers called "tombstones" are known to cause performance degradation in delete-heavy workloads.^[13] Tombstones are common in many databases, and this problem is not unique to Cassandra.

Cassandra is wide column store, and, as such, it is essentially a hybrid between a key-value and a tabular database management system. Its data model is a partitioned row store with tunable consistency.^[14] Rows are organized into tables; the first component of a table's primary key is the partition key; within a partition, rows are clustered by the remaining columns of the key.^[15] Other columns may be indexed separately from the primary key.^[16]

Tables may be created, dropped, or altered at run-time without blocking updates and queries.^[17]

Cassandra cannot execute joins or subqueries. Rather, Cassandra emphasizes denormalization through features such as collections.^[18]

A column family (called "table" since CQL 3) resembles a table in an RDBMS (Relational Database Management System). Column families contain rows and columns. Each row is uniquely identified by a row key. Each row has multiple columns, each of which has a name, value, and timestamp. Unlike a table in an RDBMS, different rows in the same column family do not have to share the same set of columns, and a column may be added to one or multiple rows at any time.^[19]

Each key in Cassandra corresponds to a value which is an object. Each key has values as columns, and these columns are grouped together into sets called column families. Thus, each key identifies a row of a variable number of elements. These column families could be considered then as tables. A table in Cassandra is a distributed multi dimensional map indexed by a key. Furthermore, applications can specify the sort order of columns within a Super Column or Simple Column family.

Cassandra is a Java-based system that can be managed and monitored via Java Management Extensions (JMX). The JMX-compliant Nodetool utility, for instance, can be used to manage a Cassandra cluster.^[20] Nodetool also offers a number of commands to return Cassandra metrics pertaining to disk usage, latency, compaction, garbage collection, and more.^[21]

Since the release of Cassandra 2.0.2 in 2013, measures of several metrics are produced via the Dropwizard metrics framework,^[22] and may be queried via JMX using tools such as JConsole or passed to external monitoring systems via Dropwizard-compatible reporter plugins.^[23]

Releases after graduation include:

• Bigtable – Original distributed database by Google
• Distributed database
• Distributed hash table (DHT)
• Dynamo (storage system) – Cassandra borrows many elements from Dynamo

Wikimedia Commons has media related to Apache Cassandra.

Wikiversity has learning resources about Big Data/Cassandra

• Lakshman, Avinash (August 25, 2008). "Cassandra - A structured storage system on a P2P Network". Engineering @ Facebook's Notes. Retrieved June 17, 2014.
• "The Apache Cassandra Project". Forest Hill, MD, USA: The Apache Software Foundation. Retrieved June 17, 2014.
• "Project Wiki". Forest Hill, MD, USA: The Apache Software Foundation. Archived from the original on June 14, 2014. Retrieved June 17, 2014.
• Hewitt, Eben (December 1, 2010). "Adopting Apache Cassandra". infoq.com. InfoQ, C4Media Inc. Retrieved June 17, 2014.
• Lakshman, Avinash; Malik, Prashant (August 15, 2009). "Cassandra - A Decentralized Structured Storage System" (PDF). cs.cornell.edu. The authors are from Facebook. Retrieved June 17, 2014.
• Ellis, Jonathan (July 29, 2009). "What Every Developer Should Know About Database Scalability". slideshare.net. Retrieved June 17, 2014. From the OSCON 2009 talk on RDBMS vs. Dynamo, Bigtable, and Cassandra.
• "Cassandra-RPM - Red Hat Package Manager (RPM) build for the Apache Cassandra project". code.google.com. Menlo Park, CA, USA: Google Project Hosting. Retrieved June 17, 2014.
• Roth, Gregor (October 14, 2012). "Cassandra by example - the path of read and write requests". slideshare.net. Retrieved June 17, 2014.
• Mansoor, Umer (November 4, 2012). "A collection of Cassandra tutorials". Retrieved February 8, 2015.
• Bushik, Sergey (October 22, 2012). "A vendor-independent comparison of NoSQL databases: Cassandra, HBase, MongoDB, Riak". NetworkWorld. Framingham, MA, USA and Staines, Middlesex, UK: IDG. Archived from the original on May 28, 2014. Retrieved June 17, 2014.