Kai is a open-source distributed key-value database, which is inspired by Amazon's Dynamo. Same as DynamoDB, it is developed for high scalability and validity of Web sites. goo home, a Japanese social networking service of more than 10 million users, is using Kai as a successful example of Kai. Because it is hard to get the search result of the Kai database through the current Web search Engine. It is suggested to search Kai with another keyword, such as erlang, sourceforge, or dynamo.


The Kai open-source project started in May 2008 and hosted on sourceforge.net. By May of 2009, 4 versions were released and the latest version is Kai-0.4.0. Most of the developers involved in the project were from Japan and the name of Kai is from the name of one of the developers' hometown.

Data Model


Kai uses a key/value data model. Any value(bit-string) can be stored with a key, which is used to retrieve the value.

Query Interface

Custom API

Kai supports basic operations(not all) of memcache API, including get(s), set, delete, quit and version. However, users cannot specify the operations' expiration time, all operation results is persistent.

Storage Architecture


Same as Amazon DynamoDB, Kai provides consistent storage in cache. It uses disk-oriented storage architecture.

Parallel Execution


The distributed structure makes Kai's requests will be distributed to N nodes in parallel. Kai uses actor model, which supported by Erlang, to collaborate with each processes with each other. One advantage of actor model is that it does not rely on shared memory, which often causes painful bugs.

Kai Logo


Source Code


Tech Docs



Hiroyuki Uchiyama

Country of Origin


Start Year


End Year


Project Type

Open Source

Written in


Embeds / Uses

Kyoto Cabinet

Inspired By


Operating Systems

BSD, Linux, Windows