Introduction to NoSQL in one page

The data model of NoSQL NoSQL emerged to solve the problem of the difficulty of running SQL on a cluster. i.e. scaling out. This leads me to think that if you can handle the amount of data, Big Data, in a single SQL box, you may not need NoSQL. Most NoSQL, as described below as type 1 to 3, is an aggregate-oriented data model, which is beneficial when running on a cluster. NoSQL types

1. Key-Value: Have metadata. e.g. Redis.
2. Document: id is a key. e.g. MongoDB
3. Column family:  Cassandra
4. Graph: Good for complex relationships. It's  ACID( atomicity, consistency, isolation, durability).

All NoSQL is schemaless. Consistency VS Availability. It's a business choice. When to use NoSQL

1. Big Data: NoSQL can run on a cluster.
2. Easy to develop: When the data model is a naturally aggregate model, NoSQL fits better than SQL.

Reference: GOTO 2012 • Introduction to NoSQL • Martin Fowler