Hanoi Key/Value Storage Engine

This storage engine implements a structure somewhat like LSM-trees (Log-Structured Merge Trees, see docs/10.1.1.44.2782.pdf). The notes in DESIGN.md describe how this storage engine work; I have not done extensive studies as how it differs from other storage mechanisms, but a brief review of available research on LSM-trees indicates that this storage engine is quite different in several respects.

Here's the bullet list:

• Insert, Delete and Read all have worst case log₂(N) complexity.
• The cost of evicting stale key/values is amortized into insertion
  • you don't need a separate eviction thread to keep memory use low
  • you don't need to schedule merges to happen at off-peak hours
• Operations-friendly "append-only" storage
  • allows you to backup live system
  • crash-recovery is very fast and the logic is straight forward
• Supports efficient range queries
• Uses bloom filters to avoid unnecessary lookups on disk
• Efficient resource utilization
  • Doesn't store all keys in memory
  • Uses a modest number of file descriptors proportional to the number of levels
  • IO is generally balanced between random and sequential
  • Low CPU overhead
• ~2000 lines of pure Erlang code in src/*.erl

How to deploy Hanoi as a Riak/KV backend

This storage engine can function as an alternative backend for Basho's Riak/KV.

You can deploy hanoi into a Riak devrel cluster using the enable-hanoi script. Clone the riak repo, change your working directory to it, and then execute the enable-hanoi script. It adds hanoi as a dependency, runs make all devrel, and then modifies the configuration settings of the resulting dev nodes to use the hanoi storage backend.

1. git clone git://github.com/basho/riak.git
2. cd riak/deps
3. git clone git://github.com/basho/hanoi.git
4. cd ..
5. ./deps/hanoi/enable-hanoi