Apache Cassandra

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Apache Cassandra
Cassandra logo
Original author(s) Avinash Lakshman, Prashant Malik
Developer(s) Apache Software Foundation
Initial release 2008
Stable release 2.0.7 / April 18, 2014 (2014-04-18)
Development status Active
Written in Java
Operating system Cross-platform
Available in English
Type Database
License Apache License 2.0
Website cassandra.apache.org

Apache Cassandra is an open source distributed 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 robust support for clusters spanning multiple datacenters,[1] with asynchronous masterless replication allowing low latency operations for all clients.

Cassandra also places a high value on performance. In 2012, University of Toronto researchers studying NoSQL systems concluded that "In terms of scalability, there is a clear winner throughout our experiments. Cassandra achieves the highest throughput for the maximum number of nodes in all experiments."[2]

Cassandra's data model is a partitioned row store with tunable consistency.[3] 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.[4] Other columns may be indexed separately from the primary key.[5]

Tables may be created, dropped, and altered at runtime without blocking updates and queries.[6]

Cassandra does not support joins or subqueries, except for batch analysis via Hadoop. Rather, Cassandra emphasizes denormalization through features like collections.[7]


Apache Cassandra was developed at Facebook to power their Inbox Search feature by Avinash Lakshman (one of the authors of Amazon's Dynamo) and Prashant Malik. It was released as an open source project on Google code in July 2008.[8] In March 2009, it became an Apache Incubator project.[9] On February 17, 2010 it graduated to a top-level project.[10]

Releases after graduation include

  • 0.6, released Apr 12 2010, added support for integrated caching, and Apache Hadoop MapReduce[11]
  • 0.7, released Jan 08 2011, added secondary indexes and online schema changes[12]
  • 0.8, released Jun 2 2011, added the Cassandra Query Language (CQL), self-tuning memtables, and support for zero-downtime upgrades[13]
  • 1.0, released Oct 17 2011, added integrated compression, leveled compaction, and improved read performance[14]
  • 1.1, released Apr 23 2012, added self-tuning caches, row-level isolation, and support for mixed ssd/spinning disk deployments[15]
  • 1.2, released Jan 2 2013, added clustering across virtual nodes, inter-node communication, atomic batches, and request tracing[16]
  • 2.0, released Sep 4 2013, added lightweight transactions, triggers, improved compactions
  • 2.0.4, released Dec 30 2013, added allowing specifying datacenters to participate in a repair, client encryption support to sstableloader, allow removing snapshots of no-longer-existing CFs[17]

Licensing and support[edit]

Apache Cassandra is an Apache Software Foundation project, so it has an Apache License (version 2.0).

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.[18] 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.
Read and write throughput both increase linearly as new machines are added, with 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
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.[3]
MapReduce support
Cassandra has Hadoop integration, with MapReduce support. There is support also for Apache Pig and Apache Hive.[19]
Query language
CQL (Cassandra Query Language) was introduced, a SQL-like alternative to the traditional RPC interface. Language drivers are available for Java (JDBC), Python (DBAPI2) and Node.JS (Helenus).

Data model[edit]

Cassandra is essentially a hybrid between a key-value and a column-oriented (or tabular) database.

A column family resembles a table in an RDBMS. 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.[20]

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.


When the cluster for Apache Cassandra is designed, an important point is to select the right partitioner. Two partitioners exist:[21]

  1. RandomPartitioner (RP): This partitioner randomly distributes the key-value pairs over the network, resulting in a good load balancing. Compared to OPP, more nodes have to be accessed to get a number of keys.
  2. OrderPreservingPartitioner (OPP): This partitioner distributes the key-value pairs in a natural way so that similar keys are not far away. The advantage is that fewer nodes have to be accessed. The drawback is the uneven distribution of the key-value pairs.

Prominent users[edit]

  • Apixio uses Cassandra to store its Patient Object Model and extracted features about patients and patient populations
  • AppScale uses Cassandra as a back-end for Google App Engine applications[22]
  • Cisco's WebEx uses Cassandra to store user feed and activity in near real time.[23]
  • The CERN ATLAS experiment uses Cassandra to archive its online DAQ system's monitoring information[24]
  • Cloudkick uses Cassandra to store the server metrics of their users.[25]
  • Constant Contact uses Cassandra in their email and social media marketing applications.[26] Over 200 nodes are deployed.
  • Digg, a large social news website, announced on Sep 9th, 2009 that it is rolling out its use of Cassandra[27] and confirmed this on March 8, 2010.[28] TechCrunch has since linked Cassandra to Digg v4 reliability criticisms and recent company struggles.[29] Lead engineers at Digg later rebuked these criticisms as red herring and blamed a lack of load testing.[30]
  • Facebook used Cassandra to power Inbox Search, with over 200 nodes deployed.[31] This was abandoned in late 2010 when they built Facebook Messaging platform on HBase.[32]
  • IBM has done research in building a scalable email system based on Cassandra.[33]
  • InWorldz has researched and developed a scalable high-performance storage system for user inventory items Cassandra.[34]
  • Netflix uses Cassandra as their back-end database for their streaming services[35][36]
  • 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[37]
  • Mahalo.com uses Cassandra to record user activity logs and topics for their Q&A website[38][39]
  • Ooyala Built a scalable, flexible, real-time analytics engine using Cassandra[40]
  • At Openwave, Cassandra acts as a distributed database and serves as a distributed storage mechanism for Openwave’s next generation messaging platform[41]
  • OpenX is running over 130 nodes on Cassandra for their OpenX Enterprise product to store and replicate advertisements and targeting data for ad delivery[42]
  • Plaxo has "reviewed 3 billion contacts in [their] database, compared them with publicly available data sources, and identified approximately 600 million unique people with contact info."[43]
  • PostRank uses Cassandra as their backend database[44]
  • Rackspace is known to use Cassandra internally.[45]
  • Reddit switched to Cassandra from memcacheDB on March 12, 2010[46] and experienced some problems in May due to insufficient nodes in their cluster.[47]
  • RockYou uses Cassandra to record every single click for 50 million Monthly Active Users in real-time for their online games[48]
  • SoundCloud uses Cassandra to store the dashboard of their users[49]
  • Talentica Software uses Cassandra as a back-end for Analytics Application with Cassandra cluster of 30 nodes and inserting around 200GB data on daily basis.[50]
  • Twitter announced it is planning to use Cassandra because it can be run on large server clusters and is capable of taking in very large amounts of data at a time.[51][52] Twitter continues to use it but not for Tweets themselves.[53]
  • Urban Airship uses Cassandra with the mobile service hosting for over 160 million application installs across 80 million unique devices[54]
  • @WalmartLabs[55] (previously Kosmix) uses Cassandra with SSD[56]
  • Yakaz uses Cassandra on a five-node cluster to store millions of images as well as its social data.[57]
  • ZangBeZang uses Cassandra as the datastore for its carrier grade recommendation and marketing platform.[58]
  • Zoho uses Cassandra for generating the inbox preview in their Zoho#Zoho Mail service

Facebook moved off its pre-Apache Cassandra deployment in late 2010 when they replaced Inbox Search with the Facebook Messaging platform.[32] In 2012, Facebook began using Apache Cassandra in its Instagram unit.[59]

Cassandra is the most popular wide column store.[60]

See also[edit]


  1. ^ Joaquin Casares (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…" 
  2. ^ Tilmann Rabl, Mohammad Sadoghi, Hans-Arno Jacobsen, Sergio Gomez-Villamor, Victor Muntes-Mulero, Serge Mankovskii (2012-08-27). "Solving Big Data Challenges for Enterprise Application Performance Management". VLDB. Retrieved 2013-07-25. "In terms of scalability, there is a clear winner throughout our experiments. Cassandra achieves the highest throughput for the maximum number of nodes in all experiments..." 
  3. ^ a b DataStax (2013-01-15). "About data consistency". Retrieved 2013-07-25. 
  4. ^ Jonathan Ellis (2012-02-15). "Schema in Cassandra 1.1". DataStax. Retrieved 2013-07-25. 
  5. ^ Jonathan Ellis (2010-12-03). "What’s new in Cassandra 0.7: Secondary indexes". DataStax. Retrieved 2013-07-25. 
  6. ^ Jonathan Ellis (2012-03-02). "The Schema Management Renaissance in Cassandra 1.1". DataStax. Retrieved 2013-07-25. 
  7. ^ Sylvain Lebresne (2012-08-05). "Coming in 1.2: Collections support in CQL3". DataStax. Retrieved 2013-07-25. 
  8. ^ James Hamilton (July 12, 2008). "Facebook Releases Cassandra as Open Source". Retrieved 2009-06-04. 
  9. ^ "Is this the new hotness now?". Mail-archive.com. 2009-03-02. Archived from the original on 25 April 2010. Retrieved 2010-03-29. 
  10. ^ "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. 
  11. ^ The Apache Software Foundation Announces Apache Cassandra Release 0.6 : The Apache Software Foundation Blog
  12. ^ The Apache Software Foundation Announces Apache Cassandra 0.7 : The Apache Software Foundation Blog
  13. ^ [Cassandra-user] [RELEASE] 0.8.0 - Grokbase
  14. ^ Cassandra 1.0.0. Is Ready for the Enterprise
  15. ^ The Apache Software Foundation Announces Apache Cassandra™ v1.1 : The Apache Software Foundation Blog
  16. ^ The Apache Software Foundation Announces Apache Cassandra™ v1.2
  17. ^ [Cassandra-user] [RELEASE] Apache Cassandra 2.0.4
  18. ^ "Deploying Cassandra across Multiple Data Centers" article on Datastax Cassandra Developer Center
  19. ^ "Hadoop Support" article on Cassandra's wiki
  20. ^ DataStax. "Apache Cassandra 0.7 Documentation - Column Families". Apache Cassandra 0.7 Documentation. Retrieved 29 October 2012. 
  21. ^ Dominic Williams. "Cassandra: RandomPartitioner vs OrderPreservingPartitioner". http://wordpress.com/: WordPress.com. Retrieved 2011-03-23. "When building a Cassandra cluster, the “key” question (sorry, that’s weak) is whether to use the RandomPartitioner (RP), or the OrderPreservingPartitioner (OPP). These control how your data is distributed over your nodes. Once you have chosen your partitioner, you cannot change without wiping your data, so think carefully! The problem with OPP: If the distribution of keys used by individual column families is different, their sets of keys will not fall evenly across the ranges assigned to nodes. Thus nodes will end up storing preponderances of keys (and the associated data) corresponding to one column family or another. If as is likely column families store differing quantities of data with their keys, or store data accessed according to differing usage patterns, then some nodes will end up with disproportionately more data than others, or serving more “hot” data than others." 
  22. ^ "Datastores on Appscale". 
  23. ^ "Re: Cassandra users survey". Mail-archive.com. 2009-11-21. Archived from the original on 17 April 2010. Retrieved 2010-03-29. 
  24. ^ "A Persistent Back-End for the ATLAS Online Information Service (P-BEAST)". 
  25. ^ 4 Months with Cassandra, a love story | Cloudkick, manage servers better
  26. ^ Klint Finley (2011-02-18). "This Week in Consolidation: HP Buys Vertica, Constant Contact Buys Bantam Live and More". Read Write Enterprise. 
  27. ^ Ian Eure. "Looking to the future with Cassandra". 
  28. ^ John Quinn. "Saying Yes to NoSQL; Going Steady with Cassandra". 
  29. ^ Erick Schonfeld. "As Digg Struggles, VP Of Engineering Is Shown The Door". 
  30. ^ "Is Cassandra to Blame for Digg v4's Failures?". 
  31. ^ "Niet compatibele browser". Facebook. Retrieved 2010-03-29. 
  32. ^ a b Kannan Muthukkaruppan. "The Underlying Technology of Messages". 
  33. ^ "Powered by Google Docs". Docs.google.com. Retrieved 2010-03-29. 
  34. ^ Dexler, Tranquillity. "InWorldz 0.7.0 R1542X". InWorldz LLC. Retrieved 9 February 2012. 
  35. ^ cite web|url=http://www.slideshare.net/adrianco/migrating-netflix-from-oracle-to-global-cassandra
  36. ^ Yury Izrailevsky (2011-01-28). "NoSQL at Netflix". 
  37. ^ Martin Cozzi (2011-08-31). "Cassandra at Formspring". 
  38. ^ "http://www.datastax.com/wp-content/uploads/2011/06/DataStax-CaseStudy-Mahalo.pdf". 
  39. ^ Watch Cassandra at Mahalo.com | DataStax Episodes | Blip
  40. ^ http://www.datastax.com/wp-content/uploads/2011/04/WP-Ooyala.pdf
  41. ^ http://www.datastax.com/wp-content/uploads/2011/05/DataStax-CaseStudy-Openwave.pdf
  42. ^ Ad Serving Technology - Advanced Optimization, Forecasting, & Targeting | OpenX
  43. ^ Preston Smalley (2011-03-20). "An important milestone - and it's only the beginning!". 
  44. ^ Ilya Grigorik (2011-03-29). "Webpulp TV: Scaling PostRank with Ilya Grigorik". 
  45. ^ "Hadoop and Cassandra (at Rackspace)". Stu Hood. 2010-04-23. Retrieved 2011-09-01. 
  46. ^ Posted by 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. 
  47. ^ Posted by 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. 
  48. ^ Dathan Vance Pattishall (2011-03-23). "Cassandra is my NoSQL Solution but". 
  49. ^ "Cassandra at SoundCloud". 
  50. ^ cite web|url=http://www.talentica.com
  51. ^ Popescu, Alex. "Cassandra @ Twitter: An Interview with Ryan King". myNoSQL. Archived from the original on 1 March 2010. Retrieved 2010-03-29. 
  52. ^ Babcock, Charles. "Twitter Drops MySQL For Cassandra - Cloud databases". InformationWeek. Archived from the original on 2 April 2010. Retrieved 2010-03-29. 
  53. ^ "Cassandra at Twitter Today". 
  54. ^ Erik Onnen. "From 100s to 100s of Millions". 
  55. ^ Walmart Labs
  56. ^ Karl Mueller. "Cassandra on SSD". 
  57. ^ "Yakaz Technologies". 
  58. ^ "ZangBeZang". 
  59. ^ Rick Branson (2013-06-26). "Cassandra at Instagram". DataStax. Retrieved 2013-07-25. 
  60. ^ DB-Engines. "DB-Engines Ranking of Wide Column Stores". 


External links[edit]