Apache CouchDB

Not to be confused withCouchbase Server.

Apache CouchDB

CouchDB's Fauxton Administration Interface, User database
Original author(s)	Damien Katz, Jan Lehnardt, Naomi Slater, Christopher Lenz, J. Chris Anderson, Paul Davis, Adam Kocoloski, Jason Davies, Benoît Chesneau, Filipe Manana, Robert Newson
Developer(s)	Apache Software Foundation
Initial release	2005(2005)
Stable release	3.3.3 / 4 December 2023(4 December 2023)
Repository	github/apache/couchdb
Written in	Erlang,JavaScript,C,C++
Operating system	Cross-platform
Type	Document-oriented database
License	Apache License 2.0
Website	couchdb.apache.org

Apache CouchDBis anopen-sourcedocument-orientedNoSQLdatabase, implemented inErlang.

CouchDB uses multiple formats and protocols to store, transfer, and process its data. It usesJSONto store data,JavaScriptas its query language usingMapReduce,andHTTPfor anAPI.

CouchDB was first released in 2005 and later became anApache Software Foundationproject in 2008.

Unlike arelational database,a CouchDB database does not store data and relationships in tables. Instead, each database is a collection of independent documents. Each document maintains its own data and self-contained schema. An application may access multiple databases, such as one stored on a user's mobile phone and another on a server. Document metadata contains revision information, making it possible to merge any differences that may have occurred while the databases were disconnected.

CouchDB implements a form ofmultiversion concurrency control(MVCC) so it does not lock the database file during writes. Conflicts are left to the application to resolve. Resolving a conflict generally involves first merging data into one of the documents, then deleting the stale one.

Other features include document-levelACIDsemantics witheventual consistency,(incremental) MapReduce, and (incremental) replication. One of CouchDB's distinguishing features ismulti-master replication,which allows it to scale across machines to build high-performance systems. A built-in Web application called Fauxton (formerly Futon) helps with administration.

History

Couchis an acronym forcluster of unreliable commodity hardware. The CouchDB project was created in April 2005 by Damien Katz, a formerLotus Notesdeveloper atIBM.He self-funded the project for almost two years and released it as an open-source project under theGNU General Public License.

In February 2008, it became an Apache Incubator project and was offered under theApache Licenseinstead.A few months after, it graduated to a top-level project.This led to the first stable version being released in July 2010.

In early 2012, Katz left the project to focus onCouchbase Server.

Since Katz's departure, the Apache CouchDB project has continued, releasing 1.2 in April 2012 and 1.3 in April 2013. In July 2013, the CouchDB community merged the codebase forBigCouch,Cloudant's clustered version of CouchDB, into the Apache project.The BigCouch clustering framework is included in the current release of Apache CouchDB.

Native clustering is supported at version 2.0.0. And the new Mango Query Server provides a simple JSON-based way to perform CouchDB queries without JavaScript or MapReduce.

Main features

ACID Semantics

CouchDB providesACIDsemantics.It does this by implementing a form ofMulti-Version Concurrency Control,meaning that CouchDB can handle a high volume of concurrent readers and writers without conflict.

Built for Offline

CouchDB can replicate to devices (like smartphones) that can go offline and handle data sync for you when the device is back online.

Distributed Architecture with Replication

CouchDB was designed with bi-directional replication (or synchronization) and off-line operation in mind. That means multiple replicas can have their own copies of the same data, modify it, and then sync those changes at a later time.

Document Storage

CouchDB stores data as "documents", as one or more field/value pairs expressed asJSON.Field values can be simple things like strings, numbers, or dates; butordered listsandassociative arrayscan also be used. Every document in a CouchDB database has a unique id and there is no required document schema.

Eventual Consistency

CouchDB guaranteeseventual consistencyto be able to provide both availability and partition tolerance.

Map/Reduce Views and Indexes

The stored data is structured using views. In CouchDB, each view is constructed by aJavaScriptfunction that acts as the Map half of amap/reduce operation. The function takes a document and transforms it into a single value that it returns. CouchDB can index views and keep those indexes updated as documents are added, removed, or updated.

HTTP API

All items have a unique URI that gets exposed via HTTP. It uses theHTTP methodsPOST, GET, PUT and DELETE for the four basicCRUD(Create, Read, Update, Delete) operations on all resources.

CouchDB also offers a built-in administration interface accessible via Web called Fauxton.

Use cases and production deployments

Replication and synchronization capabilities of CouchDB make it ideal for using it in mobile devices, where network connection is not guaranteed, and the application must keep on working offline.

CouchDB is well suited for applications with accumulating, occasionally changing data, on which pre-defined queries are to be run and where versioning is important (CRM, CMS systems, by example). Master-master replication is an especially interesting feature, allowing easy multi-site deployments.

Users

Users of CouchDB include:

• CERNuses CouchDB as database for the Data Management System at theLarge Hadron Collider.
• Red Crossuse the application iDAT for completing casework electronically in disaster areas. Here CouchDB is used as multi-node peer-to-peer offline-first database.
• IBMCloud services are based at a fundamental level on CouchDB.
• United Airlinesuses CouchDB for the in-flight entertainment systems in over 3,000 planes.
• Amadeus IT Group,for some of their back-end systems.
• Credit Suisse,for internal use at commodities department for their marketplace framework.
• Meebo,for their social platform (Web and applications).Meebo was acquired by Google and most products were shut down on July 12, 2012.
• npmuses CouchDB as replicating database for their package registry.
• Sophos,for some of their back-end systems.
• BBC,for a dynamic CMS-Platform.
• Canonicalbegan using it in 2009 for its synchronization service "Ubuntu One",but stopped using it in November 2011.
• CANAL+for international on-demand platform at CANAL+ Overseas.
• Protogrid,as storage back-end for their rapid application development framework

Data manipulation: documents and views

CouchDB manages a collection ofJSONdocuments. The documents are organised via views. Views are defined withaggregate functionsand filters are computed in parallel, much likeMapReduce.

Views are generally stored in the database and their indexes are updated continuously. CouchDB supports a view system using external socket servers and a JSON-based protocol.As a consequence, view servers have been developed in a variety of languages (JavaScript is the default, but there are also PHP, Ruby, Python and Erlang).

Accessing data via HTTP

Applications interact with CouchDB via HTTP. The following demonstrates a few examples usingcURL,a command-line utility. These examples assume that CouchDB is running onlocalhost(127.0.0.1) on port 5984.

Action	Request	Response
Accessing server information	curlhttp://127.0.0.1:5984/	{ "couchdb":"Welcome", "version":"1.1.0" }
Creating a database namedwiki	curl-XPUThttp://127.0.0.1:5984/wiki	{"ok":true}
Attempting to create a second database namedwiki	curl-XPUThttp://127.0.0.1:5984/wiki	{ "error":"file_exists", "reason":"The database could not be created, the file already exists." }
Retrieve information about thewikidatabase	curlhttp://127.0.0.1:5984/wiki	{ "db_name":"wiki", "doc_count":0, "doc_del_count":0, "update_seq":0, "purge_seq":0, "compact_running":false, "disk_size":79, "instance_start_time":"1272453873691070", "disk_format_version":5 }
Delete the databasewiki	curl-XDELETEhttp://127.0.0.1:5984/wiki	{"ok":true}
Create a document, asking CouchDB to supply a document id	curl-XPOST-H"Content-Type: application/json"--data\ '{ "text": "Wikipedia on CouchDB", "rating": 5 }'\ http://127.0.0.1:5984/wiki	{ "ok":true, "id":"123BAC", "rev":"946B7D1C" }
get a list of databases	curlhttp://127.0.0.1:5984/_all_dbs	["_replicator","_users","wiki"]

Open source components

CouchDB includes a number of other open source projects as part of its default package.

Component	Description	License
Erlang	Erlang is a general-purposeconcurrentprogramming languageandruntimesystem. The sequential subset of Erlang is afunctional languagewithstrict evaluation,single assignment,anddynamic typing	Apache 2.0(Release 18.0 and later) Erlang Public License(Earlier releases)
ICU	International Components for Unicode (ICU) is anopen-sourceproject of matureC/C++andJavalibraries forUnicodesupport, softwareinternationalizationand software globalization	Unicode License
jQuery	jQuery is a lightweightcross-browserJavaScript librarythat emphasizes interaction betweenJavaScriptandHTML	MIT License
OpenSSL	OpenSSL is anopen-sourceimplementation of theSSL and TLSprotocols. The corelibrary(written in theC programming language) implements the basiccryptographicfunctions and provides various utility functions	Apache 1.0and thefour-clause BSD License
SpiderMonkey	SpiderMonkey is a performantJavaScript enginemaintained by theMozilla Foundation.It contains aninterpreter,aJIT compilerand agarbage collector	MPL 2.0

See also

• Document-oriented database
• XML database

Bibliography

• Anderson, J. Chris; Slater, Noah; Lehnardt, Jan (November 15, 2009),CouchDB: The Definitive Guide(1st ed.),O'Reilly Media,p. 300,ISBN978-0-596-15816-3
• Lennon, Joe (December 15, 2009),Beginning CouchDB(1st ed.),Apress,p. 300,ISBN978-1-4302-7237-3,archived fromthe originalon December 5, 2010,retrievedNovember 1,2009
• Holt, Bradley (March 7, 2011),Writing and Querying MapReduce Views in CouchDB(1st ed.),O'Reilly Media,p. 76,ISBN978-1-4493-0312-9
• Holt, Bradley (April 11, 2011),Scaling CouchDB(1st ed.),O'Reilly Media,p. 72,ISBN978-1-4493-0343-3
• Brown, MC (October 31, 2011),Getting Started with CouchDB(1st ed.),O'Reilly Media,p. 50,ISBN978-1-4493-0755-4
• Thompson, Mick (August 2, 2011),Getting Started with GEO, CouchDB, and Node.js(1st ed.),O'Reilly Media,p. 64,ISBN978-1-4493-0752-3

External links

• Official website
• CouchDB: The Definitive Guide
• Complete HTTP API Reference
• Simple PHP5 library to communicate with CouchDB
• Asynchronous CouchDB client for Java
• Asynchronous CouchDB client for Scala
• Lehnardt, Jan (2008)."Couch DB at 10,000 feet".Erlang eXchange 2008.Archived fromthe originalon 9 November 2012.Retrieved15 April2012.
• Lenhardt, Jan (2009)."CouchDB for Erlang Developers".Erlang Factory London 2009.Archived fromthe originalon 19 June 2011.Retrieved15 April2012.
• Katz, Damien (January 2009)."CouchDB and Me".RubyFringe.InfoQ. Archived fromthe originalon 27 April 2011.Retrieved15 April2012.