NoSQL databases

So far there is no uniform definition of NoSQL, but most NoSQL database systems usually have the following in common:

• no relational data model

• distributed and horizontal scalability

• no or weak schema restrictions

• simple API

• no ACID, but Eventual consistency or BASE as the consistency model

NoSQL databases can be divided into

• Key-value database systems
• Column-oriented database systems
• Document-oriented database systems
• Graph database systems
• Object database systems
• XML database systems

Major concepts and technologies of NoSQL databases are

• MapReduce

• CAP theorem

• Eventual consistency and BASE

• Consistent hash function

• MVCC – Multiversion Concurrency Control

• Vector clock

• Paxos