Nice course from 10gen

10gen (maker and distributor of MongoDB) offers some very nice courses on MongoDB:
https://education.10gen.com/‎

Notes from M101J - week3:

Cool stuff about MongoDB schema

• Rich documents
• Store array of data
• Pre-join data (embed data)
• Fast access
• No "Mongo Joins"
• No constraints
• No primary key / foreign key
• Atomic transaction operation
• Within one document
• No declared schema
• Similar structure in documents

Living without transactions

• Atomic operation
• In order to accomplish it:
• restructure code to work within same document.
• Implement locking mechanism / semaphore
• Tolerate inconsistency
• One to one relationship
• Embed or not to embed depends on:
• Freq of access
• sSize of items ( > 16MB? )
• Atomicity of data
• Benefits of embedding
• Improved read performance
• One round trip to DB
• High latency: 1ms
• High bandwidth
• "Write" latency can be sig. improved by embedding data
• Decision to denormalize
• 1:1 - Embed
• 1: many - Embed (from many to 1)
• many : many - Link (using array of _id)