MongoDB是一个介于关系数据库和非关系数据库之间的产品， 是非关系数据库当中功能最丰富，最像关系数据库的。他支持的数据结构非常松散，是类似json的bjson格式，因此可以存储比较复杂的数据类型。 Mongo最大的特点是他支持的查询语言非常强大，其语法有点类似于面向对象的查询语言，几乎可以实现类似关系数据库单表查询的绝大部分功能，而且还支持 对数据建立索引。
它的特点是高性能、易部署、易使用，存储数据非常方便。主要功能特性有：
面向集合存储，易存储对象类型的数据。
模式自由。
支持动态查询。
支持完全索引，包含内部对象。
支持查询。
支持复制和故障恢复。
使用高效的二进制数据存储，包括大型对象（如视频等）。
自动处理碎片，以支持云计算层次的扩展性
支持RUBY，PYTHON，JAVA，C++，PHP等多种语言。
文件存储格式为BSON（一种JSON的扩展）
可通过网络访问
所谓“面向集合”（Collenction-Orented），意思是数据被分组存储在数据集中，被称为一个集合（Collenction)。每个 集合在数据库中都有一个唯一的标识名，并且可以包含无限数目的文档。集合的概念类似关系型数据库（RDBMS）里的表（table），不同的是它不需要定 义任何模式（schema)。
模式自由（schema-free)，意味着对于存储在mongodb数据库中的文件，我们不需要知道它的任何结构定义。如果需要的话，你完全可以把不同结构的文件存储在同一个数据库里。
存储在集合中的文档，被存储为键-值对的形式。键用于唯一标识一个文档，为字符串类型，而值则可以是各中复杂的文件类型。我们称这种存储形式为BSON（Binary Serialized dOcument Format）。
MongoDB服务端可运行在Linux、Windows或OS X平台，支持32位和64位应用，默认端口为27017。推荐运行在64位平台，因为MongoDB
在32位模式运行时支持的最大文件尺寸为2GB。
MongoDB把数据存储在文件中（默认路径为：/data/db），为提高效率使用内存映射文件进行管理。
2012-10-31 上一个版本是2012-08-29的2.2.0 这个主要是Bug修正，其他产品线还是2.0.7 1.8.5。
完全改进：
Bug
[SERVER-4781] - replica set initial sync failure when update cannot be applied to a future version of an object received via clone
[SERVER-5890] - HTTP Digest authentication doesn't work with Internet Explorer
[SERVER-6540] - queueing writebacks register with lastError too early
[SERVER-6671] - oplog is not strictly idempotent when unique index is present
[SERVER-6672] - slaveDelay Setting Causes Replica Ops to be Applied in Batches at approximately the slaveDelay Interval
[SERVER-6717] - The 'test' program does not log messages in msgasserted()
[SERVER-6810] - Memory leak in mongos when using auth
[SERVER-6821] - findAndModify update code path didn't result in splits in findAndModify2.js
[SERVER-6832] - sharding on prefix doesn't trigger "move top chunk" heuristic and causes assertion 10367
[SERVER-6834] - jstests/sharding/read_pref.js fails sometimes
[SERVER-6856] - potential out of bounds read in prefetchRecordPages()
[SERVER-6878] - distinct3.js test may leave an operation running after the test finishes; evalb does not restrict profiling query to operations the test itself generates
[SERVER-6897] - 2.2.0 upgrade of secondary of replica set with --keyfile authentication produces authentication errors - cannot upgrade without downtime
[SERVER-6902] - MongoDB 2.2 and MongoDB 2.0 cannot be mixed in sharded cluster
[SERVER-6909] - verify assertion when new version of a document is requested that does not match dotted field expression of original query; excessive logging
[SERVER-6911] - TTL monitor reports "ERROR: error processing ttl for db" during initial sync
[SERVER-6925] - DR102 too much data written uncommitted
[SERVER-6931] - warning message occasionally logged incorrectly when a client cursor is exhausted
[SERVER-6943] - addTagRegion/addShardTag fail with 3 config server sharded clusters
[SERVER-6948] - Can't call commitIfNeeded in DBDirectClient::call if not write-locked
[SERVER-6960] - Build system produces incorrect debugsymbols archive
[SERVER-6993] - findAndModify positional operator regression with undotted query fields
[SERVER-7003] - Deletions during chunk movement can cause migrations to fail
[SERVER-7004] - db.hostInfo() crashes mongod with: Uncaught std::exception: basic_string::_S_create
[SERVER-7061] - mongos can use invalid ptr to master conn when setShardVersion fails
[SERVER-7160] - Mongorestore doesn't auth against admin DB when using username and password arguments
[SERVER-7177] - state transition for replica sets isn't correct
[SERVER-7181] - Assertion: 13111:field not found, expected type 2 when an error occured during the index building phase in restore
[SERVER-7182] - Getting need to login error when trying to restore a single database
[SERVER-7186] - Batched oplog application increases frequency of idempotency violations
[SERVER-7198] - Do not go into rollback before reaching minvalid
[SERVER-7199] - Bump minvalid when recloning ops on initial sync
[SERVER-7204] - logging for shard selection for chunk migration is too verbose
[SERVER-7238] - power of 2 allocation breaks with docs > 8mb
[SERVER-7367] - Make replica set members pick up their own connection via DBDirectClient, not over the network
[SERVER-7371] - Fix corner case where an update mod is applied twice
[SERVER-7376] - migrate deletion not aggressive enough and tied to migrate moves
Improvement
[SERVER-6808] - RecoveryJob shouldn't find MMF for each entry
[SERVER-6816] - Improve journal data handling after multithreaded batch writing
[SERVER-6930] - Trim minvalid document to avoid "DFM::findAll extent empty" log messages
Task
[SERVER-7302] - Add SpiderMonkey info to THIRD-PARTY-NOTICES file
下载：32位 http://fastdl.mongodb.org/linux/mongodb-linux-i686-2.2.1.tgz
64位 http://fastdl.mongodb.org/linux/mongodb-linux-x86_64-2.2.1.tgz
源码 http://downloads.mongodb.org/src/mongodb-src-r2.2.1.tar.gz
来自:开源中国社区
