The following sources are recommended for you to study sharding in depth:
- Scaling MongoDB by Kristina Chodorow
- MongoDB: The Definitive Guide by Kristina Chodorow and Michael Dirolf
- https://docs.mongodb.com/manual/sharding/
- https://www.mongodb.com/blog/post/mongodb-16-released
- https://github.com/mongodb/mongo/blob/r3.4.2-rc0/src/mongo/s/commands/cluster_shard_collection_cmd.cpp#L469
- https://www.mongodb.com/blog/post/sharding-pitfalls-part-iii-chunk-balancing-and
- http://plusnconsulting.com/post/mongodb-sharding-and-chunks/
- https://github.com/mongodb/mongo/wiki/Sharding-Internals
- http://learnmongodbthehardway.com/schema/sharding
- http://learnmongodbthehardway.com/schema/sharding/
- https://www.infoq.com/news/2010/08/MongoDB-1.6
- http://www.pc-freak.net/images/horizontal-vs-vertical-scaling-vertical-and-horizontal-scaling-explained-diagram.png
