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Key Value Databases
A key-value database, or key-value store, is a type of NoSQL database that uses a key/value storage. This means that the data stored in the database is a collection of key-value pairs.
This type of data structure is used on many programming languages. Key-value pairs are commonly known as associative arrays, dictionaries or hash. For example, consider a dictionary of phone numbers:
| key | value |
|---|---|
| Rick | 1234555 |
| Morty | 7754321 |
| Summer | 5512377 |
The Key
The key in a key-value pair must be unique. Having a unique identifier will allow you to access the value associated with a given key.
In theory, the key can be anything you want. A key can be a string, a binary sequence, an image, among others. However, some databases may impose limitations on the type of keys that can be used.
Here are some recommendations:
- Keys should follow a convention in order to have consistency. Keys in a phone numbers dictionary should always be names, and not a combination of names, e-mail addresses and numbers.
- Keys should not be too long, or you might have performance issues.
- Keys should not be too short, or you might have readability issues.
The Value
The value in a key-value store can be anything you want. This includes strings, numbers, code, an image, a list, or even another key-value pair. Some databases allow you to restrict the data type that can be stored.
Use Cases
Key-value databases can be used on multiple scenarios. Here is a list of the most common applications:
- Telecom directories.
- User profiles and session information.
- Shopping cart contents.
- Product details or reviews.
- Internet Protocol (IP) forwarding tables.
- Services health status or configuration.
Examples
Here are some examples of databases that use the key-value approach:
- Redis
- Oracle NoSQL Database
- Cassandra (hybrid between key-value and column-oriented databases)
- Voldemort
- Consul KV store (a tool with it's own key-value store)
More Information:
- Key-value databases on Wikipedia
Key-Value database is a simple database that uses a map or a dictionary as the fundamental data model where each key is associated with one and only one value in a collection and is the most flexible type of NoSQL database.