Sunday, 1 April 2012

Write your first hadoop c++ program (WordCount)

Step 1:Write the following program using any editor then save it.
you can use vi editor.
type vi WordCount.cpp into your command script then press i to write then write it. then press esc then wq to save and quite.
// WordCount.cpp
#include "algorithm"
#include "limits"
#include "string"

#include  "stdint.h"  // <--- to prevent uint64_t errors!

#include "hadoop/Pipes.hh"
#include "hadoop/TemplateFactory.hh"
#include "hadoop/StringUtils.hh"

using namespace std;

class WordCountMapper : public HadoopPipes::Mapper {
  // constructor: does nothing
  WordCountMapper( HadoopPipes::TaskContext& context ) {

  // map function: receives a line, outputs (word,"1")
  // to reducer.
  void map( HadoopPipes::MapContext& context ) {
    //--- get line of text ---
    string line = context.getInputValue();

    //--- split it into words ---
    vector< string > words =
      HadoopUtils::splitString( line, " " );

    //--- emit each word tuple (word, "1" ) ---
    for ( unsigned int i=0; i < words.size(); i++ ) {
      context.emit( words[i], HadoopUtils::toString( 1 ) );

class WordCountReducer : public HadoopPipes::Reducer {
  // constructor: does nothing
  WordCountReducer(HadoopPipes::TaskContext& context) {

  // reduce function
  void reduce( HadoopPipes::ReduceContext& context ) {
    int count = 0;

    //--- get all tuples with the same key, and count their numbers ---
    while ( context.nextValue() ) {
      count += HadoopUtils::toInt( context.getInputValue() );

    //--- emit (word, count) ---
    context.emit(context.getInputKey(), HadoopUtils::toString( count ));

int main(int argc, char *argv[]) {
  return HadoopPipes::runTask(HadoopPipes::TemplateFactory<
                              WordCountReducer >() );
Step 2:
compile the program using g++
following is the command to compile

 g++ -I/opt/hadoop/c++/Linux-amd64-64/include -c wordcount.cpp
g++ wordcount.o -o wordcount -L/opt/hadoop/c++/Linux-amd64-64/lib -lnsl -lpthread -lhadooppipes -lhadooputils

it will create WordCount binary into your current folder.

Step 3:
Now pur this binary into hadoop hdfs by using following command:

hadoop fs -mkdir /user/test
hadoop fs -put WordCount /user/test/

Step 4:
Now make a input file for your test.
use the following command
vi input.txt
press i
write few lines
press esc then press wq.

Step 5:
keep your input inside the hadoop by using the following command:
 hadoop fs -put input.txt /user/test/

Step 6:
Now run your program using following command:

hadoop pipes -D -D -program /user/test/WordCount -input /user/test/input.txt -output /user/test/output

Hopefully it will get run now you can see your output in the output directory which we have given at the time of run /user/test/output.

to see the output type following command:

hadoop fs -text /user/test/output/part-00000

any query is welcome
good luck :)