MongoDB Document Database

MongoDB is a free and open-source document-oriented database program that stores data in flexible, JSON-like documents (BSON format) rather than in tables and rows. Developed by MongoDB Inc. (originally 10gen, founded in 2007 by Dwight Merriman, Eliot Horowitz, and Kevin Ryan in New York City), MongoDB was designed to address the scalability and flexibility limitations of traditional relational databases for modern web applications. The current version is 7.0 (2023). Key features: document model: data is stored as BSON (Binary JSON) documents, allowing nested objects, arrays, and mixed types within a single document. This flexible schema allows each document in a collection to have different fields, enabling rapid iteration during development and schema evolution without migrations. Collections: documents are grouped into collections (analogous to tables in RDBMS), but without a fixed schema. Indexes: full indexing support including single-field, compound, multi-key (array), geospatial (2d, 2dsphere), text, TTL (auto-expiring), and hashed indexes for sharding. Aggregation pipeline: a powerful data processing pipeline (db.collection.aggregate) with stages like $match, $group, $sort, $lookup (left outer join), $unwind, $project, $facet, enabling complex data transformations and analytics within the database. ACID transactions: since version 4.0, MongoDB supports multi-document ACID transactions across a replica set, and since 4.2, distributed transactions across a sharded cluster. Replication: replica sets provide automatic failover and data redundancy, with a primary node handling writes and secondary nodes replicating data asynchronously. Sharding: horizontal scaling via automatic data partitioning (shards) across multiple machines, with a sharded cluster (mongos routers, config servers, shard replica sets). Atlas: managed cloud database service on AWS, Azure, and GCP. C++ codebase. Cross-platform. SSPL (Server Side Public License) since version 4.0.