What is MongoDB ?

NOSQL

NoSQL (commonly interpreted as "not only SQL") is a broad class of database management systems, that are not primarily built on tables, and generally do not use SQL for data manipulation.
NoSQL database systems are often highly optimized for retrieve and append operations and often offer little functionality beyond record storage (e.g. key–value stores).
These next generation database system address some of the points :being non-relational, distributed, open-source, horizontally scalable, consistency and availability. The logic of validation , access control, conflict resolution, maintaining integrity constraints etc are removed from the database layer.Thus the database engine can focus on exceptional performance and scalability.

MongoDB

MongoDB is a open source document-oriented database system developed and supported by 10gen. It is a type of NoSQL database. In MongoDB data is not stored in tables as in relational database in this data is saved in collections in the form of BSON.It is has a dynamic scheme.

10gen began Development of MongoDB in October 2007. The database is used by MTV Networks, Craigslist, Foursquare and UIDAI Aadhaar. MongoDB is the one of the most popular NoSQL database management system.

Collection: A namespace within database ,that contains documents. Collection do not enforce a scheme.

Document: It is the basic unit of data in MongoDB. A document is a record in MongoDB collection. They are analogous to JSON objects but exist in the database in a more type-rich format known as BSON.
BSON: Short for binary JSON, is a binary-encoded serialization of JSON. BSON supports embedding of documents and arrays.BSON is designed to be efficient in space.

Why MongoDB ?

• Document-oriented
  • Documents (objects) map nicely to programming language data types
  • No joins and no multi-document transactions for high performance and easy scalability
• High performance
  • No joins and embedding makes reads and writes fast.
  • Indexes including indexing of keys from embedded documents and arrays.
• High availability
  • Replicated servers with automatic master failover
• Easy scalability
  • Automatic sharding (auto-partitioning of data across servers) 
  • Reads and writes are distributed over shards.
  • Eventually-consistent reads can be distributed over replicated servers
• Rich query language