What is a key-value database?

Key-value databases are a type of NoSQL databases where data is stored as pairs of 'key — value'. Each unique key corresponds to some value, which can be simple (string, number) or complex (object, list).

Features of key-value databases:

• Very high speed of read and write operations.
• Simple data structure without complex schemas.
• Well horizontally scalable.

Use cases include caching, user sessions, and storing settings.

Example of writing and reading in a key-value database (pseudocode):

db.set('user:123', {'name': 'Ivan', 'age': 30})
user = db.get('user:123')

In the context of machine learning, key-value databases can be used for quick access to model parameters, metadata, or computation results.