## rabit: Robust Allreduce and Broadcast Interface

rabit is a light weight library that provides a fault tolerant interface of Allreduce and Broadcast. It is designed to support easy implementation of distributed machine learning programs, many of which sits naturally under Allreduce abstraction.

* See the [package interface file](src/rabit.h)

Features
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* Portable library
  - Rabit is a library instead of framework, program only need to link the library to run, without restricting to a single framework.
* Flexibility in programming
  - Programs call rabit functions in any sequence, as opposed to defines limited functions and being called.
  - Program persist over all the iterations, unless it fails and recover
* Fault tolerance 
  - Rabit program can recover model and results of syncrhonization functions calls
* MPI compatible
  - Codes using rabit interface naturally compiles with existing MPI compiler
  - User can fall back to use MPI Allreduce if they like with no code modification

Design Note
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* Rabit is designed for algorithms that replicate same global model across nodes, while each node operating on local parition of data.
* The global statistics collection is done by using Allreduce

Design Goal
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* rabit should run fast
* rabit is light weight
* rabit dig safe burrows to avoid disasters