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.
git clone git://github.com/basho/riak.gitcd riak/depsgit clone git://github.com/basho/hanoi.gitcd .../deps/hanoi/enable-hanoi