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Architecture

MongoDB's architecture is designed to be flexible, scalable, and capable of handling a wide variety of data types and workloads. Below are the key components and aspects of MongoDB's architecture:

MongoDB Server​

The core component that manages the database, responsible for handling client requests, data storage, and other database operations.

Components:​

  • Mongod: The primary daemon process for the MongoDB system, handling data requests, data access, and management operations.

  • Mongos: The routing service for MongoDB Shard configurations, directing client requests to the appropriate shard.

  • Config Server: Used in sharded clusters to hold metadata and configuration settings.

Database​

A MongoDB server can host multiple databases, each acting as a high-level container for storing collections.

Components:​

  • Collections: Equivalent to tables in relational databases, collections hold the documents.

  • Documents: The basic unit of data in MongoDB, similar to a row in relational databases but more flexible.

Data Storage​

MongoDB uses a storage engine to manage how data is stored both in memory and on disk.

Components:​

  • WiredTiger: The default storage engine as of MongoDB 3.2, supporting compression and transactions.

  • MMAPv1: The original storage engine, deprecated as of MongoDB 4.0.

  • In-Memory: An engine for read-heavy workloads where data is kept in memory.

Replication​

MongoDB uses replica sets to provide high availability and data redundancy.

Components:​

  • Primary Node: The main node in a replica set, handling all write operations.

  • Secondary Nodes: Read-only nodes that replicate data from the primary node.

  • Arbiter Node: A node that participates in elections but doesn't hold data.

Sharding​

For horizontal scalability, MongoDB supports sharding, distributing data across multiple servers.

Components:​

  • Shard: A single mongod instance or replica set that holds a subset of the sharded data.

  • Chunk: A contiguous range of shard key values within a particular shard.

  • Balancer: A background process that manages the distribution of chunks in the cluster.

Indexing​

MongoDB supports various types of indexes to improve query performance.

Components:​

  • B-tree Index: The default index type, similar to those used in relational databases.

  • Geospatial Index: For querying geospatial coordinate data.

  • Text Index: For text search queries.

  • Hashed Index: For hash-based sharding.

Drivers​

MongoDB provides client libraries, known as drivers, for various programming languages like Java, Python, JavaScript, etc., to interact with the database.

Utilities​

  • Mongo Shell: An interactive JavaScript interface to MongoDB, useful for administration.

  • Mongoimport/Mongoexport: Utilities for importing and exporting data.

  • Mongodump/Mongorestore: Utilities for backup and restoration.

  • Mongostat/Mongotop: Monitoring utilities for MongoDB instances.