发布于 2015-09-14 14:48:14 | 291 次阅读 | 评论: 0 | 来源: 网络整理
This document provides a collection of hard and soft limitations of the MongoDB system.
The maximum BSON document size is 16 megabytes.
The maximum document size helps ensure that a single document cannot use excessive amount of RAM or, during transmission, excessive amount of bandwidth. To store documents larger than the maximum size, MongoDB provides the GridFS API. See mongofiles and the documentation for your driver for more information about GridFS.
在 2.2 版更改.
MongoDB supports no more than 100 levels of nesting for BSON documents.
Each namespace, including database and collection name, must be shorter than 123 bytes.
The limitation on the number of namespaces is the size of the namespace file divided by 628.
A 16 megabyte namespace file can support approximately 24,000 namespaces. Each index also counts as a namespace.
Indexed items can be no larger than 1024 bytes.
A single collection can have no more than 64 indexes.
The names of indexes, including their namespace (i.e database and collection name) cannot be longer than 128 characters. The default index name is the concatenation of the field names and index directions.
You can explicitly specify an index name to the ensureIndex() helper if the default index name is too long.
MongoDB does not support unique indexes across shards, except when the unique index contains the full shard key as a prefix of the index. In these situations MongoDB will enforce uniqueness across the full key, not a single field.
See
为片式集合强制使用唯一密钥 for an alternate approach.
There can be no more than 31 fields in a compound index.
Capped collections can hold no more than 232 documents.
Replica sets can have no more than 12 members.
Only 7 members of a replica set can have votes at any given time. See can vote Non-Voting Members for more information
The group does not work with sharding. Use mapReduce or aggregate instead.
db.eval() is incompatible with sharded collections. You may use db.eval() with un-sharded collections in a shard cluster.
$where does not permit references to the db object from the $where function. This is uncommon in un-sharded collections.
The $isolated update modifier does not work in sharded environments.
$snapshot queries do not work in sharded environments.
MongoDB only allows sharding an existing collection that holds fewer than 256 gigabytes of data.
注解
This limitation only applies to sharding collections that have existing data sets, and is not a limit on the size of a sharded collection.
MongoDB will only return sorted results on fields without an index if the sort operation uses less than 32 megabytes of memory.
You cannot use db.killOp() to kill a foreground index build.
The dot (i.e. .) character is not permissible in database names.
Database names are case sensitive even if the underlying file system is case insensitive.
在 2.2 版更改: For MongoDB instances running on Windows.
In 2.2 the following characters are not permissible in database names:
/. "*<>:|?
See Restrictions on Database Names for Windows for more information.
2.2 新版功能.
Collection names should begin with an underscore or a letter character, and cannot:
See Are there any restrictions on the names of Collections? and Restrictions on Collection Names for more information.
Field names cannot contain dots (i.e. .), dollar signs (i.e. $), or null characters. See Dollar Sign Operator Escaping for an alternate approach.