55 lines
2.6 KiB
Markdown
55 lines
2.6 KiB
Markdown
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---
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title: Key Value Databases
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---
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## Key Value Databases
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A key-value database, or key-value store, is a type of [NoSQL](https://en.wikipedia.org/wiki/NoSQL) database that uses a key/value storage. This means that the data stored in the database is a collection of key-value pairs.
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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:
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| key | value |
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|------------|-------------|
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| Rick | 1234555 |
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| Morty | 7754321 |
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| Summer | 5512377 |
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### The Key
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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.
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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.
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Here are some recommendations:
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- 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.
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- Keys should not be too long, or you might have performance issues.
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- Keys should not be too short, or you might have readability issues.
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### The Value
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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.
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### Use Cases
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Key-value databases can be used on multiple scenarios. Here is a list of the most common applications:
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- Telecom directories.
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- User profiles and session information.
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- Shopping cart contents.
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- Product details or reviews.
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- Internet Protocol (IP) forwarding tables.
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- Services health status or configuration.
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### Examples
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Here are some examples of databases that use the key-value approach:
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- [Redis](https://redis.io)
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- [Oracle NoSQL Database](https://www.oracle.com/database/nosql/index.html)
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- [Cassandra](http://cassandra.apache.org) (hybrid between key-value and column-oriented databases)
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- [Voldemort](http://www.project-voldemort.com/voldemort/)
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- [Consul KV store](https://www.consul.io/intro/getting-started/kv.html) (a tool with it's own key-value store)
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#### More Information:
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* Key-value databases on [Wikipedia](https://en.wikipedia.org/wiki/Key-value_database)
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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.
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