Lightweight MapReduce framework

Introduction

We implemented a lightweight MapReduce framework using C++. It's a cross-platform framework which has been validated on Windows(cygwin), Linux(Redhat, Ubuntu) and Mac OS. The framework itself is based on a distributed file system (like AFS) for temporary file sharing, but sshfs may work as well but not yet tested.

The final setting comes down to a cluster configuration file and a single binary executable which would ssh to other machines and call itself.

How to build

mkdir build && cd build
cmake ..
make

You will find the test binary files under test/

Configuration file

A full configuration file may look like this.

username:*
192.168.1.100 2112
192.168.1.101 2113
192.168.1.102 2113
192.168.1.102 2114

The first line consists of username and password. There are three ways to assign them.

First, if running on local machine, just put a single colon.

:
localhost 2112
127.0.0.1 2113

Second, if running on remote mahcines and with auto-login, put username:base64(password).

username:cGFzc3dvcmQ=
lab1.batman.com 2112
lab2.batman.com 2113
lab3.batman.com 2113
lab3.batman.com 2114

Third, if wanting the password prompted, put asterisk username:*.

username:*
192.168.1.100 2112
192.168.1.101 2113
192.168.1.102 2113
192.168.1.102 2114

Each line afterwards contains the ip address and the port number. No two port numbers can be the same on a single machine.

If running on remote machines, the first ip must be the master machine itself for others to connect.

Example code


### Word Counting

We have also implemented a MapReduce framework for general purposes. Users should implement their own logic by inheriting from the Mapper and Reducer classes. See example as follows.

```C++
#include "../src/mapreduce.h"

using namespace lmr;
using namespace std;

class WordCountMapper : public Mapper
{
public:
    virtual void Map(const string& key, const string& value)
    {
        int n = value.size();
        for (int i = 0; i < n; ) {
            while ((i < n) && isspace(value[i]))
                i++;

            int start = i;
            while ((i < n) && !isspace(value[i]))
                i++;

            if (start < i)
                combined_results[value.substr(start, i-start)]++;
        }
    }

    virtual void combine() {
        for (auto &p : combined_results)
            emit(p.first, to_string(p.second));
        combined_results.clear();
    }

private:
    map<string, int> combined_results;
};

REGISTER_MAPPER(WordCountMapper)

class WordCountReducer : public Reducer
{
public:
    virtual void Reduce(const string& key, ReduceInput* reduceInput)
    {
        string value;
        int result = 0;
        while (reduceInput->get_next_value(value)){
            result += stoi(value);
        }
        output(key, to_string(result));
    }
};

REGISTER_REDUCER(WordCountReducer)

int main(int argc, char **argv)
{
    MapReduceSpecification spec;
    MapReduceResult result;

    spec.program_file = basename(argv[0]);
    spec.config_file = "config.txt";
    spec.index = (argc == 2) ? atoi(argv[1]) : 0;

    spec.input_format = "input_%d.txt";
    spec.output_format = "output/result_%d.txt";
    spec.num_inputs = 3;

    spec.mapper_class = "WordCountMapper";
    spec.num_mappers = 1;

    spec.reducer_class = "WordCountReducer";
    spec.num_reducers = 2;

    MapReduce mr(&spec);
    mr.work(result);
    printf("%.3fs elapsed.\n", result.timeelapsed);

    return 0;
}

danielchristopher513 / Yet_Another_Map_Reduce_Using_CPP