In the previous section of this chapter, you learned the basics of relational databases and how to use SQL to query data. Relational data is mostly organized in a tabular form, that is, as a collection of tables with relations.
However, when the volume of data exceeds the capacity of a server, problems occur because the traditional model of relational databases does not easily support horizontal scalability, that is, storing data in a cluster of servers instead of a single one. This adds a new layer of complexibility of database management as the data is stored in a distributed form while still accessible as one logical database.
In recent years, NoSQL, or non-relational databases, have become much more popular than before due to the introduction of new database models and the remarkable performance they exhibit in big data analytics and real-time applications. Some non-relational databases are designed for high availability, scalability, and flexibility, and...