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MongoDB

MongoDB is a popular open-source NoSQL database that provides high performance, high availability, and easy scalability. It works on the concept of collections and documents rather than tables and rows.

Architecture and Data Model​

  • Documents: Data is stored in BSON (Binary JSON) format, which allows for complex, hierarchical data structures.
  • Collections: Equivalent to tables in relational databases, collections group related documents. Documents within a collection do not need to share the same structure (schema-less or flexible schema).
  • Replica Sets: MongoDB provides high availability through Replica Sets, which are groups of MongoDB servers that maintain the same data set, providing redundancy and automatic failover.
  • Sharding: MongoDB scales horizontally using sharding, distributing data across multiple machines based on a shard key.

Installation​

MongoDB is typically not included in the default OS repositories. You must add the official MongoDB repository.

Example for Ubuntu:

  1. Import the public key used by the package management system.
  2. Create a list file for MongoDB.
  3. Reload local package database.
  4. Install the MongoDB packages: sudo apt install -y mongodb-org
  5. Start the service: sudo systemctl start mongod

Basic Operations​

Access the MongoDB shell using the mongosh (MongoDB Shell) command.

mongosh

Common Commands​

  • Show Databases: show dbs
  • Use/Create Database: use my_app_db (Creates the DB implicitly when data is inserted).
  • Insert Document: 
    db.users.insertOne({ name: "Alice", age: 28, city: "New York" })
  • Find Documents:
    • Find all: db.users.find()
    • Find specific: db.users.find({ age: { $gt: 25 } }) (Find users older than 25)
  • Update Document: 
    db.users.updateOne({ name: "Alice" }, { $set: { city: "Boston" } })
  • Delete Document: 
    db.users.deleteOne({ name: "Alice" })

Configuration and Best Practices​

Configuration is stored in /etc/mongod.conf.

  • Security: By default, MongoDB does not enable authentication. It is critical to enable it in a production environment.
    1. Create an administrative user.
    2. Enable authorization in mongod.conf (security.authorization: enabled).
    3. Restart the mongod service.
  • Network Binding: Ensure MongoDB binds only to necessary interfaces (net.bindIp). Do not expose it to the public internet without proper authentication and firewalls.
  • Indexing: Just like relational databases, MongoDB requires indexes for efficient querying. Ensure queries are supported by appropriate indexes using the .explain() method.
  • Storage Engine: The default storage engine is WiredTiger, which provides document-level concurrency and compression.