CouchDB

CouchDB ("**c**luster **o**f **u**nreliable **c**ommodity **h**ardware") is a document-oriented NoSQL DBMS.

History

CouchDB was created by Damien Katz in April 2005, it was initially written in C++ and used the GNU General Public License. CouchDB then discarded C++ and moved to Erlang for development in February 2006. CouchDB became an Apache Incubator project and converted its license to Apache License in February 2008. The beta version 0.10.0 of CouchDB published in October 2009. The CouchDB published 1.2.0 in April 2012, 1.3.0 in April 2013, 1.4.0 in August 2013, 1.5.0 in November 2013, 1.6.0 in June 2014. In September 2016, CouchDB published 2.0.0, the prime feature of this version is that it support for clustering, this work is originally done in the BigCouch project, and it was merged into the 2.0.0 version of CouchDB. The latest version of CouchDB is 2.3.0 in December 2018.

Checkpoints

Non-Blocking

In CouchDB, any changes to a document simply appends a new record to the database file, it is always non-blocking to take a snapshot of the file system to get the latest version of the database.

Compression

Naïve (Record-Level)

CouchDB does compaction operation to reduce the disk usage similar like the vacuum in SQLite. CouchDB support user-defined number of revisions. The compaction operations can either be manually triggered or automatically.

Concurrency Control

Multi-version Concurrency Control (MVCC)

The CouchDB uses Multi-version Concurrency Control (MVCC) as the concurrency control policy for read operations, each clients sees a consistent snapshot during the read operation.

Indexes

B+Tree

The documents in CouchDB are indexed by their name and sequence id, these index are organized by B-trees.

Isolation Levels

Snapshot Isolation

In CouchDB, a read request will always see the most recent snapshot of the database at the time of the beginning of the request because of MVCC.

Joins

Not Supported

The data in CouchDB are store as documents, which is unnecessary for joins operations. The way to replace join operation is to do denormalization or stored with related data in documents.

Logging

Shadow Paging

CouchDB uses shadow paging as its logging method, it only does appending operations to the current database file, which provides the MVCC features.

Query Interface

HTTP / REST

CouchDB provide RESTful HTTP API as its query interface.

Storage Architecture

Disk-oriented

CouchDB store its data on disk and all update are synchronously flushed to disk.

Storage Model

Custom

The storage model of CouchDB is simply a large file, this database file contains variable-length data chunks, and a custom file critical header. As the CouchDB is append-only, the header of the database file is in the tail of the file to be access or re-append by each append operation.

Storage Organization

Copy-on-Write / Shadow Paging

CouchDB implements append-only B+Tree and uses copy-on-write method to update the database file as well as the index.

Stored Procedures

Not Supported

System Architecture

Shared-Nothing

CouchDB can provide the same version of replica in different peer, therefore, woyeach peer can provide same data for user to access. They do not share anything.

CouchDB Logo
Website

http://couchdb.apache.org/

Source Code

https://github.com/apache/couchdb

Tech Docs

http://docs.couchdb.org/en/stable/index.html

Developer

Damien Katz

Country of Origin

US

Start Year

2005

Acquired By

Apache Software Foundation

Project Type

Open Source

Written in

Erlang

Supported languages

C, C#, Erlang, Haskell, Java, JavaScript, Lisp, Lua, Objective-C, Ocaml, Perl, PHP, PL/SQL, Python, Ruby, Smalltalk

Operating Systems

Android, BSD, iOS, Linux, OS X, Solaris, Windows

Licenses

Apache v2

Wikipedia

https://en.wikipedia.org/wiki/Apache_CouchDB