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Video: How do NoSQL databases work?

https://www.youtube.com/watch?v=0buKQHokLK8

Relational Databases (MySQL, etc.)

• Built to store relational data as efficiently as possible

• Relational data: data with predefined relationships 

• Hard to scale - resource intensive

• Can scale vertically, not horizontally

Why do NoSQL databases scale so well

• Do away with costly relationships

• Every item stands on their own

• Essentially key value stores

• Value can be json data storing more data

• Can split workload across multiple servers

• These parts of database are called partitions

• Key determines on which partition data is stored

• Primary key

• Hash function to convert each item's primary key into number that falls into fixed range - hash value and ranged used to determine where to store item

• Range is called a Keyspace

• Where to store new items, where to find existing ones

NosQL are Schemaless

• Items in database don't need to have same structure

• In Relational database, have to define table's structure, and each item must conform to it

• No structure is good if data is constantly evolving

NoSQL vs Relational

• Can only retrieve by primary key

• NoSQL databases are eventually consistent