Key-Value Databases Examples and Comparison

We compare hereafter three examples of key-value databases: Redis, Riak and Voldemort. All of those three solutions provide scalability, fault tolerance and a near-linear increase in performance.

Riak is based on a simple and symmetric architecture and is designed for highly distributed environments such as the cloud. Like Voldemort, Riak relies on a consistent hashing. It incorporates map-reduce programming modelthat split the work to multiple tasks over several cluster nodes.

In Riak, any node can respond to a client request. In order to track system status, Riak do not rely on a unique node. Instead, it relies on a gossip protocol between the nodes to track nodes status (nodes that are alive, nodes that hold data). Riak provides high fault-tolerance but with less performance than Redis.

Indeed, Redis is more suitable for time-critical applications because it relies on in-memory dataset for fast responses. Like other key-value stores, Redis enables simple operations such as to insert, delete and lookup. Similar to Voldemort, Redis allows users to associate lists and sets not only with a blob (large data objects) or a string but also with a key. It also enables list and set operations.

Redis is appropriate to handle rapidly changing data such as real-time data collection from sensors and real-time communications. On the other hand, Voldermort is suitable for very large datasets such as geological data and meta-data of maps. Indeed, it can support the storage of huge volumes without a great impact on performance.

Experiments showed that Redis scales when increasing datasets volumes but it does not scale with the increasing number of nodes. On the contrary, Voldemort scales when the number of nodes increases but it does not scale with the increasing size of datasets. Redisensures better data availability compared to Voldermort. However, both of them show a reduced availability when having to deal with very large datasets. It has been also shown that adding nodes to Voldermort system helps to enhance its availability Summarises the important features of Redis, Riak and Voldemort.