In DDS 4.0, the system collection includes the following:
admin.system.roles - Store role definition
admin.system.users - Store user definition
admin.system.version - Store cluster/replica set version information
local.startup_log - Store startup log
config.system.sessions - Store session information
config.transactions - Store transaction information
config.settings - Store settings
config.databases - Store database definition
config.collections - Store collection definition
config.views - Store view definition
config.minversions - Store the smallest document version in the database
config.fns - Store DBRef related information
config.oplog.$main - ops log main collection
config.oplog.rs - ops log replica set specific
config.oplog.local - ops log mongos specific
[database name].system.namespaces - Store namespace information
[database name].system.indexes - Store index definition
[database name].system.js - Store MR/ such as programs
[database name].system.profile - Store profile information
[database name].system.users - Store database user information