42 lines
1.8 KiB
Markdown
42 lines
1.8 KiB
Markdown
# Hanoi Key/Value Storage Engine
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This storage engine implements a structure somewhat like LSM-trees
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(Log-Structured Merge Trees, see docs/10.1.1.44.2782.pdf). The notes in
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DESIGN.md describe how this storage engine work; I have not done extensive
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studies as how it differs from other storage mechanisms, but a brief review of
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available research on LSM-trees indicates that this storage engine is quite
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different in several respects.
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Here's the bullet list:
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- Insert, Delete and Read all have worst case log<sub>2</sub>(N) complexity.
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- The cost of evicting stale key/values is amortized into insertion
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- you don't need a separate eviction thread to keep memory use low
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- you don't need to schedule merges to happen at off-peak hours
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- Operations-friendly "append-only" storage
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- allows you to backup live system
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- crash-recovery is very fast and the logic is straight forward
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- Supports efficient range queries
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- Uses bloom filters to avoid unnecessary lookups on disk
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- Efficient resource utilization
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- Doesn't store all keys in memory
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- Uses a modest number of file descriptors proportional to the number of levels
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- IO is generally balanced between random and sequential
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- Low CPU overhead
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- ~2000 lines of pure Erlang code in src/*.erl
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### How to deploy Hanoi as a Riak/KV backend
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This storage engine can function as an alternative backend for Basho's Riak/KV.
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You can deploy `hanoi` into a Riak devrel cluster using the `enable-hanoi`
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script. Clone the `riak` repo, change your working directory to it, and then
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execute the `enable-hanoi` script. It adds `hanoi` as a dependency, runs `make
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all devrel`, and then modifies the configuration settings of the resulting dev
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nodes to use the hanoi storage backend.
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1. `git clone git://github.com/basho/riak.git`
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1. `cd riak/deps`
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1. `git clone git://github.com/basho/hanoi.git`
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1. `cd ..`
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1. `./deps/hanoi/enable-hanoi`
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