A key-value database is a type of NoSQL database which uses a key-value method to store data. Key-value databases work differently from the relational databases. They store data as a collection of key-value pairs where a key serves as a unique identifier. The key-value databases are designed for storing, retrieving, and managing a data structure known as a hash table (or dictionaries). They contain objects or records. Which records have different fields within them. These records can be retrieved using a key to quickly find the data within the database. The strength is in scalability and parallel processing. They are unsuitable for complex relational queries. They are designed to provide API for data analytics. They are simple and fast in proper use case.
In some situations, we use a datastore like a file system. In such a case, we can look up records using keys.
A key-value store or document-oriented database is practical in such a situation. We already know some of the key-value-store DB engines, such as ElasticSearch. They let us create parallel search structures which help analyze things like the log files, you can think about the ELK stack. We need a relational database when we need inter-record joins. In these use cases, we do not need joins. In these scenarios, we actually can use something like the PostgreSQL JSON functionality or equivalent functionality in MySQL. But for various specific use cases, we need some named key-value database. The key-value pair is a concept in some of the programming languages. Phone directory, IP forwarding table, stock ticker are some typical examples used to explain the fields of application.
The key in a key-value pair should be a unique identifier which will allow us to access the value associated with that key. The implementation of a key depends on the database. The value in a key-value store can be anything. It can be a text, a chunk of HTML or a PHP snippet or a file such as an image. The typical usage of the key-value database is in image stores, object cache, key-based file systems and so on.
Redis is another well known example of a key-value database. The use case of various key-value database widely varies. Other some examples are Apache Ignite, Couchbase Server, Dynamo, memcached and so on.