MongoDB Documentation, Release 3.0.4 Behavioral Changes Windows Specific Changes Chapter 12. Release Notes 904 $^{833}$https://jira.mongodb.org/browse/SERVER-4442 $^{834}$https://jira.mongodb.org/browse/SERVER-4584 $^{835}$https://jira.mongodb.org/browse/SERVER-6729 $^{836}$https://jira.mongodb.org/browse/SERVER-5516 $^{837}$https://jira.mongodb.org/browse/SERVER-2238 $^{838}$https://jira.mongodb.org/browse/SERVER-828 $^{839}$https://jira.mongodb.org/browse/SERVER-5648 Windows XP is Not Supported As of 2.2, MongoDB does not support Windows XP. Please upgrade to a more recent version of Windows to use the latest releases of MongoDB. See SERVER-5648 839 for more information. New $elemMatch Projection Operator The $elemMatch operator allows applications to narrow the data re- turned from queries so that the query operation will only return the first matching element in an array. See the $elemMatch reference and the SERVER-2238 837 and SERVER-828 838 issues for more information. _id Fields and Indexes on Capped Collections All capped collections now have an _id field by default, if they exist outside of the local database, and now have indexes on the _id field. This change only affects capped collections created with 2.2 instances and does not affect existing capped collections. See: SERVER-5516 836 for more information. Change the name of these databases before upgrading. See SERVER-4584 834 and SERVER-6729 835 for more infor- mation. The names of the data files include the database name. If you attempt to upgrade a database instance with one or more of these characters, mongod will refuse to start. Restrictions on Database Names for Windows Database names running on Windows can no longer contain the following characters: /\. " * <>:|? See the SERVER-4442 833 and the Are there any restrictions on the names of Collections? (page 753) FAQ item. Collections names may have any other valid UTF-8 string. These new restrictions are in addition to the existing restrictions on collection names which are: This change does not affect collections created with now illegal names in earlier versions of MongoDB. Restrictions on Collection Names In version 2.2, collection names cannot: • contain the $ . • be an empty string (i.e. "" ). • A collection name should begin with a letter or an underscore. • A collection name cannot contain the null character. • Begin with the system. prefix. MongoDB reserves system. for system collections, such as the system.indexes collection. • The maximum size of a collection name is 128 characters, including the name of the database. However, for maximum flexibility, collections should have names less than 80 characters.