Key-Value Databases

Key: value → The access mechanism is the key → High performance!

Redis

→ Key-value NoSQL DB → Open source → Can be scaled horizontally in a distributed mode → Automatically partition data to other nodes

The Big-O notation

• O (1): time for the operation always constant
• O (n): time for the operation linearly proportional to the data it contains
• O (LogN): ...
• O (NlogN): ...
• O (Log N+M): …

Data Structures

• String: Most generic data type, can store anything. Until 512MB

→ Key → String → Hash: Allows multiple keys → List: Order preserved and acessed by LPOP and RPOP → Set: Order not preserved. Do not allow duplicates → Sorted set → Hyperloglog → Geo: Coordinates. GIS. Extension of the sorted list. → Pub sub → Transaction

Modelling in Key-Value Databases

→ Redis as primary database → Redis are cache (fast memory access)