NoSQL

Why NoSQL

• If the data to be stored is unstructured
• If there's a need to serialise and deserialise data
• If the size of the data to be stored is large
• Favour eventual consistency
• limited by the scale

BASE

• Basically available - the system guarantees availability.
• Soft state - the state of the system may change over time, even without input.
• Eventual consistency - the system will become consistent over a period of time, given that the system doesn't receive input during that period.

Key-Value store

• Redis, DynamoDB
  • For rapidly changing data
• Just like an hash-map
  • flat in nature
  • used for session oriented applications
• Maintain keys in lexicographic order, allowing efficient retrieval of key ranges.

Document Store

• MongoDB
  • For high flexibility, and occasionally changing data
• such in JSON, XML, binary formate
  • key points to a hierarchical structure
  • unstructured catalog data
• Provides APIs or a query language to query based on internal structure of the document itself

Wide Column Store

- Cassandra, Bigtable
- high availability and high scalability

• for large volume of write
• don't need to update and read a lot
  

Graph database

• network structure such as social media networks
  • social applications
• Most can only access with REST APIs