System Collections

Synopsis

MongoDB stores system information in collections that use the <database>.system.* namespace, which MongoDB reserves for internal use. Do not create collections that begin with system.

MongoDB also stores some additional instance-local metadata in the local database local.replset.* namespace, specifically for replication purposes and in the config database for sessions information.

MongoDB Atlas and other MongoDB cloud services store essential operational data in dedicated databases that use the prefix __mdb_internal_*. Do not access or modify databases with this prefix. We recommend that you ignore these namespaces in administrative tools. For more information on these cloud-specific databases, see Internal Databases.

Collections

System collections include these collections stored in the admin database:

admin.system.roles

The admin.system.roles collection stores custom roles that administrators create and assign to users to provide access to specific resources.

admin.system.users

The admin.system.users collection stores the user's authentication credentials as well as any roles assigned to the user. Users may define authorization roles in the admin.system.roles collection.

admin.system.version

The admin.system.version collection stores metadata to support internal operations. Do not modify this collection unless specifically instructed to in this documentation or by a MongoDB support engineer.

System collections include these collections stored in the config database:

config.system.indexBuilds

The indexBuilds collection stores information related to in-progress index builds.

config.system.preimages

Stores previous versions of modified documents from collections with the changeStreamPreAndPostImages option enabled. The config.system.preimages collection is automatically purged when the pre-images expire. For details, see changeStreamOptions.preAndPostImages.expireAfterSeconds.