NoSQL families

NoSQL is an umbrella term for databases that don’t use the traditional relational model of tables and joins, usually to scale out across many machines or fit a particular kind of data. Key-value stores like Redis map a key to a blob, about as fast and simple as it gets. Document stores like MongoDB keep nested JSON-like records, so related data lives together. Wide-column stores like Cassandra spread huge tables of rows keyed by a partition across many machines, built for heavy write loads. Graph databases like Neo4j store nodes and the links between them for relationship-heavy queries. Each gives up some flexibility, typically joins or ad-hoc queries, to be very good at one access pattern.