An experimentation to add ORM on top of Tokyo Cabinet 

What Is Tokyo Cabinet?
- Modern implementation of DBM(key/value hash style(HDB), but supports fixed length hash(FDB), and b tree(BDB))
- High concurrency/ high scalability (developed by a developer at Mixi, Japanese equivalent of Facebook)
- More detail at http://tokyocabinet.sourceforge.net/index.html

How dm-tokyo-cabinet-adapter stores data into Tokyo Cabinet.

- Each object is stored as "ObjName.bdb" file: object id as key and entire data marshalled as value
- Each attribute is stored as "ObjNameAttribute.bdb" file: attribute name as key and reference object id as value
- The above architecture can also be considerd "ObjeName.bdb" as table and "ObjNameAttribute.bdb" as indexes for each attributes.
- Currently implements basic CRUD, association, and eql finder.

Motivation behind the development.

- To experiment what you can do with basic hash based database. 
  Interesting post at http://groups.google.com/group/merb/browse_thread/thread/a8c6b154576c6270
- To learn internal of DataMapper and how to implement ORM/adapter 

How to install

1. Install Tokyo Cabinet http://tokyocabinet.sourceforge.net
2. Install Ruby Binding  http://tokyocabinet.sourceforge.net/rubydoc/
3. Install dm-tokyo-cabinet-adapter
3.1 download dm-tokyo-cabinet-adapter
3.2 cd to the dir
3.3 gem build dm-tokyo-cabinet-adapter.gemspec 
3.4 gem install dm-tokyo-cabinet-adapter-0.0.2.gem
4. Create data dir
5. Setup database.yml like below

:development: 
  :adapter: tokyo_cabinet
  :data_path: <%= Pathname(__FILE__).dirname.expand_path + 'data' %>

6. The rest is usual way to setup datamapper on Merb.

Benchmarking results
http://gist.github.com/25946

My current implementation is a lot slower than MySQL and sqlite, but changing some data storage strategies speed up the performance dramatically, so there are lots of potential for optimization. 

Further research topics/TODO
- Implement outstanding tasks such as multi conditions, other finder conditions (<, <=, like), Data Types
- At this moment, it's only uses B tree, as it covers the wide range of functionality (range search, duplicate values, transaction support, and so on). Consider replacing part to HDB or FDB for compact storage and speed.
- Are there any ways to retrieve first/last key on FDB/HDB?
- Can TC support "not equal" operation?