Key-value databases

Key-value databases, such as Redis, Oracle Berkley DB, and Voldemort, employ a simple key-value data model to store data as a collection of unique keys mapped to value objects. This is illustrated in the following table that maps session IDs for web applications to session data:

Key-value data structures are found in many programming languages where they are commonly referred to as dictionaries or hash maps. Key-value databases extend these data structures through their ability to partition and scale horizontally across a cluster, thereby effectively providing huge distributed dictionaries. Key-value databases are particularly useful as a means to improve the performance and throughput of systems that are required to handle potentially millions of requests per second. Examples of use cases include popular e-commerce websites, storing session data for web applications, and facilitating caching layers.