The fashionable sense of NoSQL, which dates from 2009, refers to databases that aren’t constructed on relational tables, in contrast to SQL databases. Typically, NoSQL databases boast higher design flexibility, horizontal scalability, and better availability than conventional SQL databases, typically at the price of weaker consistency.

NoSQL databases can take a lot of kinds. They are often cloud providers or set up on-premises. They’ll assist a number of knowledge fashions: key-value, doc, column, graph, and typically even relational—which is one cause that NoSQL is usually parsed as “Not Solely SQL.” They’ll additionally assist a variety of consistency fashions, from robust consistency to eventual consistency.

Key-value is essentially the most primary of the 4 non-relational knowledge fashions. Generally different database fashions are carried out on high of a key-value basis layer.

Column databases have keys, values, and timestamps; the timestamp is used for figuring out the legitimate content material. Cassandra is a distinguished instance of a column database.

[ Also on InfoWorld: The best distributed relational databases. ]