Gossamr lets you run your Go programs on Hadoop.

Quick Example

Oh, man. Illustrating MapReduce with a word count? Get out of town.

package main

import (
  "log"
  "strings"

  "github.com/vistarmedia/gossamr"
)

type WordCount struct{}

func (wc *WordCount) Map(p int64, line string, c gossamr.Collector) error {
  for _, word := range strings.Fields(line) {
    c.Collect(strings.ToLower(word), int64(1))
  }
  return nil
}

func (wc *WordCount) Reduce(word string, counts chan int64, c gossamr.Collector) error {
  var sum int64
  for v := range counts {
    sum += v
  }
  c.Collect(sum, word)
  return nil
}

func main() {
  wordcount := gossamr.NewTask(&WordCount{})

  err := gossamr.Run(wordcount)
  if err != nil {
    log.Fatal(err)
  }
}

Running with Hadoop

./bin/hadoop jar ./contrib/streaming/hadoop-streaming-1.2.1.jar \
  -input /mytext.txt \
  -output /output.15 \
  -mapper "gossamr -task 0 -phase map" \
  -reducer "gossamr -task 0 -phase reduce" \
  -io typedbytes \
  -file ./wordcount
  -numReduceTasks 6