The majority of the NoSQL databases described in this study are key/value stores at their core habitually providing additional functionality for access by secondary values. Voldemort is a key-value storage system used in LinkedIn. Examples of key/value databases without additional indexing facilities are:
• Berkeley DB
• MemcacheDB
• Redis
• Tokyo Cabinet/Tyrant
• Risk
The Pros and Cons of Key/Value Databases are:
Pros:
• Very fast
• Very scalable
• Simple model
• Able to distribute horizontally
Cons:
• Many data structures (objects), hence cannot be easily modeled
as key–value pairs