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There are a number of btree (and variants) implementations around, but for
many reasons like complexity and tight coupling with external code bases, or
licensing issues, to find an easy to embed implementation of an on disk btree
is not an easy task.
Since an on disk btree is a tool useful in a number of software projects this
library is an attempt to bring to the table an open implementation of a btree.
The term "open" here means: simple to use, BSD licensed, well documented, and
simple to modify and understand.
Currently this is a work in progress, so far we have a subset of basic btree
operations implemented on top of an on disk allocator (something like a
file-based malloc).
Supported operations are adding new keys, splitting of nodes.
Deletion is not supported, nor update of old values.
In other words the project is NOT usable so far, more work is needed.
Currently everything is written on disk on every write for the sake of
simplicity of the first implementation, but the work is in progress in order
to cache the allocator metadata in memory, so that the performances can be
The goal is to eventually support all the following features:
- A compromise between fast implementation and ability to incrementally reclaim
memory from disk automatically. This is why we have the on disk allocator.
- Range queries using 128 bit precision integers, to use the btree as index.
- Good tools for recovering and checking the btree.
- Good documentation.
Perhaps in the future:
- Optional append only mode with compaction, for higher corruption resistance.
In the first stage of the project the goal is to be good enough for the Redis
project (in order to use this library for the diskstore feature of Redis).
However while trying to reach this goal every care will be used in order to
retain a great level of generality of this lib that will continue to live as a
stand alone library. Redis will just happen to use a copy of it.