MongoDB Atlas and other cloud services like MongoDB Search store essential operational data in dedicated databases within your cluster. These databases use specific, reserved prefixes to clearly separate internal service data from your user data.
Important
Do not access or modify databases with the prefix __mdb_internal_.
The primary naming convention for databases reserved for internal use by MongoDB Atlas and other cloud services is __mdb_internal_<service-name>. You could impact the stability and availability of your services if you modify these databases. We recommend that you ignore these namespaces in administrative tools.
The following internal databases may be present in your cluster:
__mdb_internal_atlas: Used by Atlas for internal operations, including an automated test workload that runs on every replica set and sharded cluster to measure read/write availability.__mdb_internal_search: Used by MongoDB Search to store its catalog information. This database may be present in self-hosted, community deployments that use MongoDB Search.
To learn more about internal databases and collections reserved for the core MongoDB Server, see System Collections.