Apache Cassandra

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Apache Cassandra
Original author(s)Avinash Lakshman, Prashant Malik / Facebook
Developer(s)Apache Software Foundation
Initial releaseJuly 2008; 16 years ago (2008-07)
Written inJava
Operating systemCross-platform
Available inEnglish
TypeNoSQL Database, data store
LicenseApache License 2.0

Apache Cassandra is a free and open-source, distributed, wide-column store, NoSQL, database management system designed to handle large amounts of data across multiple commodity servers, providing availability with no single point of failure. Cassandra supports clusters and spanning of multiple data centers[1] with asynchronous and master-less replication. It allows low latency operations for all clients. Cassandra implements a combination of Amazon's Dynamo distributed storage and replication techniques combined with Google's Bigtable data and storage engine model.[2]

History

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.[3] In March 2009, it became an Apache Incubator project.[4] On February 17, 2010, it graduated to a top-level project.[5]

Facebook developers named their database after the Trojan mythological prophet Cassandra, with classical allusions to a curse on an oracle.[6]

Releases

Releases after graduation include

  • 0.6, released April 12, 2010, added support for integrated caching, and Apache Hadoop MapReduce[7]
  • 0.7, released January 8, 2011, added secondary indexes and online schema changes[8]
  • 0.8, released June 2, 2011, added the Cassandra Query Language (CQL), self-tuning memtables, and support for zero-downtime upgrades[9]
  • 1.0, released October 17, 2011, added integrated compression, leveled compaction, and improved read-performance[10]
  • 1.1, released April 23, 2012, added self-tuning caches, row-level isolation, and support for mixed ssd/spinning disk deployments[11]
  • 1.2, released January 2, 2013, added clustering across virtual nodes, inter-node communication, atomic batches, and request tracing[12]
  • 2.0, released September 4, 2013, added lightweight transactions (based on the Paxos consensus protocol), triggers, improved compaction
  • 2.1 released September 10, 2014[13]
  • 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.[14]
  • 3.11 released June 23th, 2017 as a stable 3.11 release series and bug fix from the last tick-tock feature release.
  • 4.0 released July 26, 2021.
  • 4.1 released December 13th, 2022.
  • 4.1.4 released February 14, 2024.
  • 5.0 released September 5, 2024.
Version Original release date Latest version Release date Status[15]
Old version, no longer maintained: 0.6 2010-04-12 0.6.13 2011-04-18 No longer maintained
Old version, no longer maintained: 0.7 2011-01-10 0.7.10 2011-10-31 No longer maintained
Old version, no longer maintained: 0.8 2011-06-03 0.8.10 2012-02-13 No longer maintained
Old version, no longer maintained: 1.0 2011-10-18 1.0.12 2012-10-04 No longer maintained
Old version, no longer maintained: 1.1 2012-04-24 1.1.12 2013-05-27 No longer maintained
Old version, no longer maintained: 1.2 2013-01-02 1.2.19 2014-09-18 No longer maintained
Old version, no longer maintained: 2.0 2013-09-03 2.0.17 2015-09-21 No longer maintained
Old version, no longer maintained: 2.1 2014-09-16 2.1.22 2020-08-31 No longer maintained
Old version, no longer maintained: 2.2 2015-07-20 2.2.19 2020-11-04 No longer maintained
Old version, no longer maintained: 3.0 2015-11-09 3.0.29 2023-05-15 No longer maintained
Old version, no longer maintained: 3.11 2017-06-23 3.11.15 2023-05-05 No longer maintained
Old version, yet still maintained: 4.0 2021-07-26 4.0.13 2023-05-20 Maintained until 5.1.0 release
Old version, yet still maintained: 4.1 2022-06-17 4.1.6 2024-08-19 Maintained until 5.2.0 release
Current stable version: 5.0 2024-09-05 5.0 2024-09-05 Latest release. Maintained until 5.3.0 release
Legend:
Old version, not maintained
Old version, still maintained
Latest version
Latest preview version
Future release

Main features

Distributed
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.[16] 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 fail over and disaster recovery.
Scalability
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.
Fault-tolerant
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,[17] 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.[18]
MapReduce support
Cassandra has Hadoop integration, with MapReduce support. There is support also for Apache Pig and Apache Hive.[19]
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

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++.[20]

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:[21] <syntaxhighlight lang="mysql"> 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; </syntaxhighlight> Which gives: <syntaxhighlight lang="text"> 

id | lastName | firstName

+----------+---------- 

 1 | Doe      | John

(1 rows) </syntaxhighlight>

Known issues

Up to Cassandra 1.0, Cassandra was not row-level consistent,[22] 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. 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.[23]

Cassandra is not supported on Windows as of version 4, see issue CASSANDRA-16171.[24]

Tombstones

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

Data model

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.[18] 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, or 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 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 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.

Management and monitoring

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 the release of 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]

See also

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References

  1. ^ Casares, Joaquin (November 5, 2012). "Multi-datacenter Replication in Cassandra". DataStax. Retrieved July 25, 2013. Cassandra's innate datacenter concepts are important as they allow multiple workloads to be run across multiple datacenters...
  2. ^ "Apache Cassandra Documentation Overview". Retrieved January 21, 2021.
  3. ^ Hamilton, James (July 12, 2008). "Facebook Releases Cassandra as Open Source". Retrieved June 4, 2009.
  4. ^ "Is this the new hotness now?". Mail-archive.com. March 2, 2009. Archived from the original on April 25, 2010. Retrieved March 29, 2010.
  5. ^ "Cassandra is an Apache top level project". Mail-archive.com. February 18, 2010. Archived from the original on March 28, 2010. Retrieved March 29, 2010.
  6. ^ "The meaning behind the name of Apache Cassandra". Archived from the original on November 1, 2016. Retrieved July 19, 2016. 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[.]
  7. ^ "The Apache Software Foundation Announces Apache Cassandra Release 0.6 : The Apache Software Foundation Blog". April 13, 2010. Retrieved January 5, 2016.
  8. ^ "The Apache Software Foundation Announces Apache Cassandra 0.7 : The Apache Software Foundation Blog". January 11, 2011. Archived from the original on March 4, 2016. Retrieved January 5, 2016.
  9. ^ Eric Evans. "[Cassandra-user] [RELEASE] 0.8.0". Archived from the original on June 8, 2015. Retrieved January 5, 2016.
  10. ^ "Cassandra 1.0.0. Is Ready for the Enterprise". InfoQ. Retrieved January 5, 2016.
  11. ^ "The Apache Software Foundation Announces Apache Cassandra™ v1.1 : The Apache Software Foundation Blog". April 24, 2012. Retrieved January 5, 2016.
  12. ^ "The Apache Software Foundation Announces Apache Cassandra™ v1.2 : The Apache Software Foundation Blog". apache.org. January 2, 2013. Retrieved December 11, 2014.
  13. ^ Sylvain Lebresne (September 10, 2014). "[VOTE SUCCESS] Release Apache Cassandra 2.1.0". mail-archive.com. Retrieved December 11, 2014.
  14. ^ "Cassandra 2.2, 3.0, and beyond". June 16, 2015. Archived from the original on April 20, 2016. Retrieved April 22, 2016.
  15. ^ "Cassandra Server Releases". cassandra.apache.org. Retrieved December 15, 2015.
  16. ^ "Deploying Cassandra across Multiple Data Centers". DataStax. Retrieved December 11, 2014.
  17. ^ "The CAP Theorem - Learn Cassandra". teddyma.gitbooks.io.
  18. ^ 18.0 18.1 DataStax (January 15, 2013). "About data consistency". Archived from the original on July 26, 2013. Retrieved July 25, 2013.
  19. ^ "Hadoop Support" Archived 2017-11-16 at the Wayback Machine article on Cassandra's wiki
  20. ^ "DataStax C/C++ Driver for Apache Cassandra". DataStax. Retrieved December 15, 2014.
  21. ^ "CQL". Archived from the original on January 13, 2016. Retrieved January 5, 2016.
  22. ^ "WAT - Cassandra: Row level consistency #$@&%*! - datanerds.io". datanerds.io. Archived from the original on November 26, 2016. Retrieved November 28, 2016.
  23. ^ Lebresne, Sylvain (February 21, 2012). "Coming up in Cassandra 1.1: Row Level Isolation". DataStax: always-on data platform | NoSQL | Apache Cassandra. Retrieved July 18, 2018.
  24. ^ "Remove Windows scripts". Cassandra issue tracker. April 4, 2023. Retrieved April 4, 2023.
  25. ^ Rodriguez, Alain (July 27, 2016). "About Deletes and Tombstones in Cassandra".
  26. ^ Ellis, Jonathan (February 15, 2012). "Schema in Cassandra 1.1". DataStax. Retrieved July 25, 2013.
  27. ^ Ellis, Jonathan (December 3, 2010). "What's new in Cassandra 0.7: Secondary indexes". DataStax. Retrieved July 25, 2013.
  28. ^ Ellis, Jonathan (March 2, 2012). "The Schema Management Renaissance in Cassandra 1.1". DataStax. Retrieved July 25, 2013.
  29. ^ Lebresne, Sylvain (August 5, 2012). "Coming in 1.2: Collections support in CQL3". DataStax. Retrieved July 25, 2013.
  30. ^ DataStax. "Apache Cassandra 0.7 Documentation - Column Families". Apache Cassandra 0.7 Documentation. Retrieved October 29, 2012.
  31. ^ "NodeTool". Cassandra Wiki. Archived from the original on January 13, 2016. Retrieved January 5, 2016.
  32. ^ "How to monitor Cassandra performance metrics". Datadog. December 3, 2015. Retrieved January 5, 2016.
  33. ^ "Metrics". Cassandra Wiki. Archived from the original on November 12, 2015. Retrieved January 5, 2016.
  34. ^ "Monitoring". Cassandra Documentation. Retrieved February 1, 2018.

Bibliography

External links

Wikimedia Commons has media related to Apache Cassandra.
Wikiversity has learning resources about Big Data/Cassandra
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