Redis, an in-memory key value data store. It comes under the category of NoSQL or Non Relational Database where storing, manipulating and retrieving of data in Redis doesn't require and use any SQL or Relations (Tables).
Relational Databases look at solving real world domain representation inside computers using a Relation/Table. A Relation/Table is a Set where the following properties are guaranteed.
Furthermore relational databases allow to define constraints within and among relations. These constraints can be;
On top of this there is a language called Structured Query Language which is a standardized way of Retrieving, Manipulating of data in those Relation/Table.
With the growth of high volume websites such as Twitter, Facebook and the emergence of IAAS (Infrastructure As A Service) solutions such as Amazon AWS, which uses distributed data centers around the globe, the need for NoSQL databases are ever so high! This is because issuing of a single SQL which covers data in across multiple data centers in different countries is not possible. Furthermore relational databases depends a lot on JOINs and distributed data centers pose a problem to this also.
Redis, on the other hand doesn't use SQL or Relation/Table. Redis has built-in data structures and algorithms to solve frequently faced design issues.
Redis has Key/Value, Lists, Hashes (Maps), Set and Sorted Set data structures.
To get started with Redis in Ubuntu;