Apache Cassandra

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Apache Cassandra
Cassandra logo
Original author(s)Avinash Lakshman, Prashant Malik / Facebook
Developer(s)Apache Software Foundation
Initial releaseJuly 2008; 13 years ago (2008-07)
Stable release
4.0.1[1] Edit this on Wikidata / 7 September 2021; 36 days ago (7 September 2021)
Written inJava
Operating systemCross-platform
Available inEnglish
TypeNoSQL Database, data store
LicenseApache License 2.0
Websitecassandra.apache.org Edit this on Wikidata

Apache Cassandra is a free and open-source, distributed, wide-column store, NoSQL database management system designed to handle large amounts of data across many commodity servers, providing high availability with no single point of failure. Cassandra offers support for clusters spanning multiple datacenters,[2] with asynchronous masterless replication allowing low latency operations for all clients. Cassandra was designed to implement a combination of Amazon's Dynamo distributed storage and replication techniques combined with Google's Bigtable data and storage engine model.[3]


Avinash Lakshman, one of the authors of Amazon's Dynamo, and Prashant Malik initially developed Cassandra at Facebook to power the Facebook inbox search feature. Facebook released Cassandra as an open-source project on Google code in July 2008.[4] In March 2009 it became an Apache Incubator project.[5] On February 17, 2010 it graduated to a top-level project.[6]

Facebook developers named their database after the Trojan mythological prophet Cassandra, with classical allusions to a curse on an oracle.[7]


Releases after graduation include

  • 0.6, released Apr 12 2010, added support for integrated caching, and Apache Hadoop MapReduce[8]
  • 0.7, released Jan 08 2011, added secondary indexes and online schema changes[9]
  • 0.8, released Jun 2 2011, added the Cassandra Query Language (CQL), self-tuning memtables, and support for zero-downtime upgrades[10]
  • 1.0, released Oct 17 2011, added integrated compression, leveled compaction, and improved read-performance[11]
  • 1.1, released Apr 23 2012, added self-tuning caches, row-level isolation, and support for mixed ssd/spinning disk deployments[12]
  • 1.2, released Jan 2 2013, added clustering across virtual nodes, inter-node communication, atomic batches, and request tracing[13]
  • 2.0, released Sep 4 2013, added lightweight transactions (based on the Paxos consensus protocol), triggers, improved compactions
  • 2.1 released Sep 10 2014[14]
  • 2.2 released July 20, 2015
  • 3.0 released November 11, 2015
  • 3.1 through 3.10 releases were monthly releases using a tick-tock-like release model, with even-numbered releases providing both new features and bug fixes while odd-numbered releases will include bug fixes only.[15]
  • 3.11 released June 23, 2017 as a stable 3.11 release series and bug fix from the last tick-tock feature release.
  • 4.0 released July 26, 2021.
  • 4.0.1 released September 7, 2021.
Version Original release date Latest version Release date Status[16]
Old version, no longer maintained: 0.6 2010-04-12 0.6.13 2011-04-18 No longer supported
Old version, no longer maintained: 0.7 2011-01-10 0.7.10 2011-10-31 No longer supported
Old version, no longer maintained: 0.8 2011-06-03 0.8.10 2012-02-13 No longer supported
Old version, no longer maintained: 1.0 2011-10-18 1.0.12 2012-10-04 No longer supported
Old version, no longer maintained: 1.1 2012-04-24 1.1.12 2013-05-27 No longer supported
Old version, no longer maintained: 1.2 2013-01-02 1.2.19 2014-09-18 No longer supported
Old version, no longer maintained: 2.0 2013-09-03 2.0.17 2015-09-21 No longer supported
Old version, no longer maintained: 2.1 2014-09-16 2.1.22 2020-08-31 No longer supported
Older version, yet still maintained: 2.2 2015-07-20 2.2.19 2020-11-04 Still supported, critical fixes only
Older version, yet still maintained: 3.0 2015-11-09 3.0.24 2021-02-28 Still supported
Older version, yet still maintained: 3.11 2017-06-23 3.11.10 2021-02-28 Still supported
Current stable version: 4.0 2021-07-26 4.0.1 2021-09-07 Latest release
Old version
Older version, still maintained
Latest version
Latest preview version
Future release

Main features[edit]

Every node in the cluster has the same role. There is no single point of failure. Data is distributed across the cluster (so each node contains different data), but there is no master as every node can service any request.
Supports replication and multi data center replication
Replication strategies are configurable.[17] Cassandra is designed as a distributed system, for deployment of large numbers of nodes across multiple data centers. Key features of Cassandra’s distributed architecture are specifically tailored for multiple-data center deployment, for redundancy, for failover and disaster recovery.
Designed to have read and write throughput both increase linearly as new machines are added, with the aim of no downtime or interruption to applications.
Data is automatically replicated to multiple nodes for fault-tolerance. Replication across multiple data centers is supported. Failed nodes can be replaced with no downtime.
Tunable consistency
Cassandra is typically classified as an AP system, meaning that availability and partition tolerance are generally considered to be more important than consistency in Cassandra,[18] Writes and reads offer a tunable level of consistency, all the way from "writes never fail" to "block for all replicas to be readable", with the quorum level in the middle.[19]
MapReduce support
Cassandra has Hadoop integration, with MapReduce support. There is support also for Apache Pig and Apache Hive.[20]
Query language
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).
Eventual consistency
Cassandra manages eventual consistency of reads, upserts and deletes through Tombstones.

Cassandra Query Language[edit]

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++.[21]

The keyspace in Cassandra is a namespace that defines data replication across nodes. Therefore, replication is defined at the keyspace level. Below an example of keyspace creation, including a column family in CQL 3.0:[22]

  WITH REPLICATION = { 'class' : 'SimpleStrategy', 'replication_factor' : 3 };

USE MyKeySpace;

CREATE COLUMNFAMILY MyColumns (id text, Last text, First text, PRIMARY KEY(id));

INSERT INTO MyColumns (id, Last, First) VALUES ('1', 'Doe', 'John');

SELECT * FROM MyColumns;

Which gives:

 id | Last | First
  1 | Doe  | John

(1 rows)

Known issues[edit]

Up to Cassandra 1.0, Cassandra was not row level consistent,[23] meaning that inserts and updates into the table that affect the same row that are processed at approximately the same time may affect the non-key columns in inconsistent ways. 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.[24]


Deletion markers called "Tombstones" are known to cause severe performance degradation.[25]

Data model[edit]

Cassandra is wide column store, and, as such, essentially a hybrid between a key-value and a tabular database management system. Its data model is a partitioned row store with tunable consistency.[19] 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.[26] Other columns may be indexed separately from the primary key.[27]

Tables may be created, dropped, and altered at run-time without blocking updates and queries.[28]

Cassandra cannot do joins or subqueries. Rather, Cassandra emphasizes denormalization through features like collections.[29]

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 a 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.[30]

Each key in Cassandra corresponds to a value which is an object. Each key has values as columns, and 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.

Management and monitoring[edit]

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 (adding nodes to a ring, draining nodes, decommissioning nodes, and so on).[31] Nodetool also offers a number of commands to return Cassandra metrics pertaining to disk usage, latency, compaction, garbage collection, and more.[32]

Since Cassandra 2.0.2 in 2013, measures of several metrics are produced via the Dropwizard metrics framework,[33] and may be queried via JMX using tools such as JConsole or passed to external monitoring systems via Dropwizard-compatible reporter plugins.[34]

Notable applications[edit]

According to DB-Engines ranking, Cassandra is the most popular wide column store,[35] and in September 2014 became the 9th most popular database.[36]

  • Apple uses 100,000 Cassandra nodes, as revealed at Cassandra Summit San Francisco 2015,[37] although it has not elaborated for which products, services or features.
  • AppScale uses Cassandra as a back-end for Google App Engine applications[38]
  • BlackRock uses Cassandra in their Aladdin investment management platform[39][40]
  • CERN used Cassandra-based prototype for its ATLAS experiment to archive the online DAQ system's monitoring information[41]
  • Cisco's WebEx uses Cassandra to store user feed and activity in near real time.[42]
  • Constant Contact uses Cassandra in their email and social media marketing applications.[43] Over 200 nodes are deployed.
  • Digg, a social news website, announced on Sep 9th, 2009 that it is rolling out its use of Cassandra[44] and confirmed this on March 8, 2010.[45] TechCrunch has since linked Cassandra to Digg v4 reliability criticisms and recent company struggles.[46] A lead engineer at Digg later rebuked these criticisms in a social media post as red herring and blamed a lack of load testing.[47]
  • Discord switched to Cassandra to store billions of messages from MongoDB in November, 2015[48]
  • Formspring uses Cassandra to count responses, as well as store social graph data (followers, following, blockers, blocking) for 26 Million accounts with 10 million responses a day[49]
  • Globo.com uses Cassandra as a back-end database for their streaming services[50]
  • Grubhub uses Cassandra as their primary persistent data store for their backend services.[51]
  • Mahalo.com used Cassandra to record user activity logs and topics for their Q&A website[52][53]
  • Monzo, a UK Bank, uses Cassandra for almost all of their persistent data storage.[54][55]
  • Netflix uses Cassandra as their back-end database for their streaming services[56][57]
  • Nutanix appliances use Cassandra to store metadata and stats.[58]
  • Ooyala built a real-time analytics engine using Cassandra[59]
  • Openwave uses Cassandra as a distributed database and as a distributed storage mechanism for their messaging platform[60]
  • OpenX is running over 130 nodes on Cassandra for their OpenX Enterprise product to store and replicate advertisements and targeting data for ad delivery[61]
  • Rackspace uses Cassandra internally.[62]
  • Reddit switched to Cassandra from memcacheDB on March 12, 2010[63] and experienced some problems in May of that year due to insufficient nodes in their cluster.[64]
  • RockYou uses Cassandra to record every single click for 50 million Monthly Active Users in real-time for their online games[65]
  • SoundCloud uses Cassandra to store the dashboard of their users[66]
  • Uber uses Cassandra to store around 10,000 features in their daily updated company-wide Feature Store for low-latency access during live model predictions[67]
  • Urban Airship uses Cassandra with the mobile service hosting for over 160 million application installs across 80 million unique devices[68]

See also[edit]


  1. ^ https://github.com/apache/cassandra/releases/tag/cassandra-4.0.1.
  2. ^ Casares, Joaquin (2012-11-05). "Multi-datacenter Replication in Cassandra". DataStax. Retrieved 2013-07-25. Cassandra’s innate datacenter concepts are important as they allow multiple workloads to be run across multiple datacenters…
  3. ^ "Apache Cassandra Documentation Overview". Retrieved 2021-01-21.
  4. ^ Hamilton, James (July 12, 2008). "Facebook Releases Cassandra as Open Source". Retrieved 2009-06-04.
  5. ^ "Is this the new hotness now?". Mail-archive.com. 2009-03-02. Archived from the original on 25 April 2010. Retrieved 2010-03-29.
  6. ^ "Cassandra is an Apache top level project". Mail-archive.com. 2010-02-18. Archived from the original on 28 March 2010. Retrieved 2010-03-29.
  7. ^ "The meaning behind the name of Apache Cassandra". Archived from the original on 2016-11-01. Retrieved 2016-07-19. Apache Cassandra is named after the Greek mythological prophet Cassandra. [...] Because of her beauty Apollo granted her the ability of prophecy. [...] When Cassandra of Troy refused Apollo, he put a curse on her so that all of her and her descendants' predictions would not be believed. [...] Cassandra is the cursed Oracle[.]
  8. ^ "The Apache Software Foundation Announces Apache Cassandra Release 0.6 : The Apache Software Foundation Blog". Retrieved 5 January 2016.
  9. ^ "The Apache Software Foundation Announces Apache Cassandra 0.7 : The Apache Software Foundation Blog". Retrieved 5 January 2016.
  10. ^ Eric Evans. "[Cassandra-user] [RELEASE] 0.8.0". Archived from the original on 8 June 2015. Retrieved 5 January 2016.
  11. ^ "Cassandra 1.0.0. Is Ready for the Enterprise". InfoQ. Retrieved 5 January 2016.
  12. ^ "The Apache Software Foundation Announces Apache Cassandra™ v1.1 : The Apache Software Foundation Blog". Retrieved 5 January 2016.
  13. ^ "The Apache Software Foundation Announces Apache Cassandra™ v1.2 : The Apache Software Foundation Blog". apache.org. Retrieved 11 December 2014.
  14. ^ Sylvain Lebresne (10 September 2014). "[VOTE SUCCESS] Release Apache Cassandra 2.1.0". mail-archive.com. Retrieved 11 December 2014.
  15. ^ "Cassandra 2.2, 3.0, and beyond". 16 June 2015. Retrieved 22 April 2016.
  16. ^ "Cassandra Server Releases". cassandra.apache.org. Retrieved 15 December 2015.
  17. ^ "Deploying Cassandra across Multiple Data Centers". DataStax. Retrieved 11 December 2014.
  18. ^ "The CAP Theorem - Learn Cassandra". teddyma.gitbooks.io.
  19. ^ a b DataStax (2013-01-15). "About data consistency". Archived from the original on 2013-07-26. Retrieved 2013-07-25.
  20. ^ "Hadoop Support" Archived 2017-11-16 at the Wayback Machine article on Cassandra's wiki
  21. ^ "DataStax C/C++ Driver for Apache Cassandra". DataStax. Retrieved 15 December 2014.
  22. ^ "CQL". Archived from the original on 13 January 2016. Retrieved 5 January 2016.
  23. ^ "WAT - Cassandra: Row level consistency #$@&%*! - datanerds.io". datanerds.io. Retrieved 28 November 2016.
  24. ^ Lebresne, Sylvain (2012-02-21). "Coming up in Cassandra 1.1: Row Level Isolation". DataStax: always-on data platform | NoSQL | Apache Cassandra. Retrieved 2018-07-18.
  25. ^ Rodriguez, Alain (27 Jul 2016). "About Deletes and Tombstones in Cassandra".
  26. ^ Ellis, Jonathan (2012-02-15). "Schema in Cassandra 1.1". DataStax. Retrieved 2013-07-25.
  27. ^ Ellis, Jonathan (2010-12-03). "What's new in Cassandra 0.7: Secondary indexes". DataStax. Retrieved 2013-07-25.
  28. ^ Ellis, Jonathan (2012-03-02). "The Schema Management Renaissance in Cassandra 1.1". DataStax. Retrieved 2013-07-25.
  29. ^ Lebresne, Sylvain (2012-08-05). "Coming in 1.2: Collections support in CQL3". DataStax. Retrieved 2013-07-25.
  30. ^ DataStax. "Apache Cassandra 0.7 Documentation - Column Families". Apache Cassandra 0.7 Documentation. Retrieved 29 October 2012.
  31. ^ "NodeTool". Cassandra Wiki. Archived from the original on 13 January 2016. Retrieved 5 January 2016.
  32. ^ "How to monitor Cassandra performance metrics". Datadog. 3 December 2015. Retrieved 5 January 2016.
  33. ^ "Metrics". Cassandra Wiki. Retrieved 5 January 2016.
  34. ^ "Monitoring". Cassandra Documentation. Retrieved 1 February 2018.
  35. ^ DB-Engines. "DB-Engines Ranking of Wide Column Stores".
  36. ^ DB-Engines. "DB-Engines Ranking".
  37. ^ Luca Martinetti: Apple runs more than 100k [production] Cassandra nodes. on Twitter
  38. ^ "Datastores on Appscale". Archived from the original on 2013-09-07. Retrieved 2011-07-07.
  39. ^ "Top Cassandra Summit Sessions For Advanced Cassandra Users". Archived from the original on 2017-03-08. Retrieved 2015-12-20.
  40. ^ "Multi-Tenancy in Cassandra at BlackRock".
  41. ^ A Persistent Back-End for the ATLAS Online Information Service (P-BEAST). 2012.
  42. ^ "Re: Cassandra users survey". Mail-archive.com. 2009-11-21. Archived from the original on 17 April 2010. Retrieved 2010-03-29.
  43. ^ Finley, Klint (2011-02-18). "This Week in Consolidation: HP Buys Vertica, Constant Contact Buys Bantam Live and More". Read Write Enterprise.
  44. ^ Eure, Ian. "Looking to the future with Cassandra".
  45. ^ Quinn, John. "Saying Yes to NoSQL; Going Steady with Cassandra". Archived from the original on 2012-03-07.
  46. ^ Schonfeld, Erick. "As Digg Struggles, VP Of Engineering Is Shown The Door".
  47. ^ "Is Cassandra to Blame for Digg v4's Failures?".
  48. ^ Vishnevskiy, Stanislav (2017-01-14). "How Discord Stores Billions of Messages". Discord Blog. Retrieved 2019-07-02.
  49. ^ Cozzi, Martin (2011-08-31). "Cassandra at Formspring".
  50. ^ Nunes, Alexandre (2016-06-22). "Cassandra At The Heart Of Globo's Live Streaming Platform".
  51. ^ Blackie, William (2018-07-26). "Cloud infrastructure at Grubhub". Grubhub Bytes. Retrieved 2019-03-29.
  52. ^ "Mahalo.com powered by Apache Cassandra™" (PDF). DataStax.com. Santa Clara, CA, USA: DataStax. 2012-04-10. Archived from the original (PDF) on 2014-12-17. Retrieved 2014-06-13.
  53. ^ Watch Cassandra at Mahalo.com |DataStax Episodes |Blip Archived 2011-12-10 at the Wayback Machine
  54. ^ "We had issues with Monzo on 29th July. Here's what happened, and what we did to fix it". Monzo. Retrieved 2020-12-09.
  55. ^ "We secured thousands of Cassandra clients to keep Monzo's data safe". Monzo. Retrieved 2020-12-09.
  56. ^ Cockcroft, Adrian (2011-07-11). "Migrating Netflix from Datacenter Oracle to Global Cassandra". slideshare.net. Retrieved 2014-06-13.
  57. ^ Izrailevsky, Yury (2011-01-28). "NoSQL at Netflix".
  58. ^ "Nutanix Bible". Archived from the original on 2015-12-10. Retrieved 2015-04-18.
  59. ^ Ooyala (2010-05-18). "Designing a Scalable Database for Online Video Analytics" (PDF). DataStax.com. Mountain View CA, USA. Archived from the original (PDF) on 2014-12-17. Retrieved 2014-06-14.
  60. ^ Mainstay LLC (2013-11-11). "DataStax Case Study of Openwave Messaging" (PDF). DataStax.com. Santa Clara, CA, USA: DataStax. Archived from the original (PDF) on 2014-09-07. Retrieved 2014-06-15.
  61. ^ Ad Serving Technology - Advanced Optimization, Forecasting, & Targeting |OpenX Archived 2011-10-07 at the Wayback Machine
  62. ^ "Hadoop and Cassandra (at Rackspace)". Stu Hood. 2010-04-23. Retrieved 2011-09-01.
  63. ^ david [ketralnis] (2010-03-12). "what's new on reddit: She who entangles men". blog.reddit. Archived from the original on 25 March 2010. Retrieved 2010-03-29.
  64. ^ the reddit admins at (2010-05-11). "blog.reddit -- what's new on reddit: reddit's May 2010 "State of the Servers" report". blog.reddit. Archived from the original on 14 May 2010. Retrieved 2010-05-16.
  65. ^ Pattishall, Dathan Vance (2011-03-23). "Cassandra is my NoSQL Solution but".
  66. ^ "Cassandra at SoundCloud". Archived from the original on 2013-09-05. Retrieved 2013-07-15.
  67. ^ Hermann, Jeremy (5 September 2017). "Meet Michelangelo: Uber's Machine Learning Platform".
  68. ^ Onnen, Erik (19 July 2011). "From 100s to 100s of Millions".


External links[edit]