MongoDB Concepts

Note

MongoDB Fundamentals

Default Architecture

Connections

• Refers to a client connection to a MongoDB server or replica set/cluster
• Gives you access to all databases hosted on that server

Database

• A logical namespace for collections
• They are isolation units with their own collections, indexes, access permissions.

Collections

• Analogous to a Relational DB table
• Belong to ONLY ONE DATABASE.

Documents

Analogous to Records/Rows in a Relational DB table

Default Databases

• admin Database: This database is crucial for administrative operations. It stores user authentication information, roles, and other administrative settings. It’s essential for managing your MongoDB server and should NOT be deleted.  
• config Database: In a sharded cluster (a more advanced MongoDB setup for handling large datasets), the config database stores metadata about the cluster’s configuration, including shard information and chunk distribution. If you’re not using sharding (which is typical for local development), this database is generally not actively used but it’s still best to leave it alone. Deleting it could cause issues if you later decide to implement sharding.
• local Database: This database is used for local server information, such as oplog (operation log) data, which is important for replication. For single-server local development, this database is also not strictly necessary but it’s best to leave it untouched. Deleting it won’t cause immediate problems in a simple setup, but it’s a core part of MongoDB’s internal workings.

CAUTION

It’s strongly recommended NOT to delete the admin, config, or local databases. They are part of MongoDB’s internal structure and are used for various functionalities, even in a local development environment. Deleting them could lead to unexpected behavior or issues if you later decide to use more advanced MongoDB features.