It is a short introduction to NoSQL Databases that is freely available thanks to Christoph Strauch.

Follows the Table of Content:

• Introduction
• The NoSQL-Movement
• Basic Concepts, Techniques and Patterns
• Key-/Value-Stores
• Document Databases
• Column-Oriented Databases
• Conclusion
• Further Reading, Listening and Watching

Follows the link down below:

• http://www.christof-strauch.de/nosqldbs.pdf

Comment

After checking the references, it was written probably at the end of 2011.
You will not find more recent techniques about Distributed HashTables/Storages/BlockChains, Graph Databases, or more recent NoSQL libraries such as LevelDB or RocksDB.
Still a good little book with well digested content.