【IT168 资讯】Apache CouchDB 是一个面向文档的数据库管理系统。它提供以 JSON 作为数据格式的 REST 接口来对其进行操作，并可以通过视图来操纵文档的组织和呈现。 CouchDB 是 Apache 基金会的优异开源项目。
CouchDB落实到最底层的数据结构就是两类B+Tree 。
▲Apache CouchDB
与现在流行的关系数据库服务器不同，CouchDB 是围绕一系列语义上自包含的文档而组织的。 CouchDB 中的文档是没有模式的(schema free)，也就是说并不要求文档具有某种特定的结构。 CouchDB 的这种特性使得相对于传统的关系数据库而言，有自己的适用范围。一般来说，围绕文档来构建的应用都比较适合使用 CouchDB 作为其后台存储。 CouchDB 强调其中所存储的文档，在语义上是自包含的。这种面向文档的设计思路，更贴近很多应用的问题域的真实情况。对于这类应用，使用 CouchDB 的文档来进行建模，会更加自然和简单。与此同时，CouchDB 也提供基于 MapReduce 编程模型的视图来对文档进行查询，可以提供类似于关系数据库中 SQL 语句的能力。 CouchDB 对于很多应用来说，提供了关系数据库之外的更好的选择。
项目地址：http://couchdb.apache.org/
CouchDB 1.1.1 改进记录：
* Support SpiderMonkey 1.8.5
* Add configurable maximum to the number of bytes returned by _log.
* Allow CommonJS modules to be an empty string.
* Bump minimum Erlang version to R13B02.
* Do not run deleted validate_doc_update functions.
* ETags for views include current sequence if include_docs=true.
* Fix bug where duplicates can appear in _changes feed.
* Fix bug where update handlers break after conflict resolution.
* Fix bug with _replicator where include "filter" could crash couch.
* Fix crashes when compacting large views.
* Fix file descriptor leak in _log
* Fix missing revisions in _changes?style=all_docs.
* Improve handling of compaction at max_dbs_open limit.
* JSONP responses now send "text/javascript" for Content-Type.
* Link to ICU 4.2 on Windows.
* Permit forward slashes in path to update functions.
* Reap couchjs processes that hit reduce_overflow error.
* Status code can be specified in update handlers.
* Support provides() in show functions.
* _view_cleanup when ddoc has no views now removes all index files.
* max_replication_retry_count now supports "infinity".
* Fix replication crash when source database has a document with empty ID.
* Fix deadlock when assigning couchjs processes to serve requests.
* Fixes to the document multipart PUT API.
* Fixes regarding file descriptor leaks for databases with views.
* Add configurable maximum to the number of bytes returned by _log.
* Allow CommonJS modules to be an empty string.
* Bump minimum Erlang version to R13B02.
* Do not run deleted validate_doc_update functions.
* ETags for views include current sequence if include_docs=true.
* Fix bug where duplicates can appear in _changes feed.
* Fix bug where update handlers break after conflict resolution.
* Fix bug with _replicator where include "filter" could crash couch.
* Fix crashes when compacting large views.
* Fix file descriptor leak in _log
* Fix missing revisions in _changes?style=all_docs.
* Improve handling of compaction at max_dbs_open limit.
* JSONP responses now send "text/javascript" for Content-Type.
* Link to ICU 4.2 on Windows.
* Permit forward slashes in path to update functions.
* Reap couchjs processes that hit reduce_overflow error.
* Status code can be specified in update handlers.
* Support provides() in show functions.
* _view_cleanup when ddoc has no views now removes all index files.
* max_replication_retry_count now supports "infinity".
* Fix replication crash when source database has a document with empty ID.
* Fix deadlock when assigning couchjs processes to serve requests.
* Fixes to the document multipart PUT API.
* Fixes regarding file descriptor leaks for databases with views.
