timothy

timothy: Node.js library for writing Hadoop MapReduce jobs in JS

Timothy's primary goal is to make Hadoop's Yellow Elephant rich and famous.

Installation

npm install timothy

Basic Example

    // require timothy
    require('timothy')
        // basic configuration for the job: hadoop conf, input, output, name, etc
        .configure({	
             hadoopHome: "/path/to/hadoop/home" // this can be provided from environment
             config: "./hadoop.xml",
             input:  "/test.txt",
             output: "/processed_"+(new Date().getTime()),
             name:   "Timothy Word Count Example",
             "mapred.map.tasks": 10 // properties can also be passed
        })
        // map function: one (line) or two (key, value) arguments
        .map(function(line){
            var words = line.split(" ");
            for(var i=0; i<words.length; i++)
                this.emit(words[i], 1); // this.emit is used to generate output
        })
        // reduce function: two arguments (key, value)
        .reduce(function(word,counts){
            emit(word, counts.length); // emit is part of object so can be called without the 'this' qualification
        })
        // run function, creates the job, uploads it and blocks until 
        // the execution has finished
        .run();

Testing in the local machine

    require('timothy')
        .map(function(line){
            var words = line.split(" ");
            for(var i=0; i<words.length; i++)
                this.emit(words[i], 1);
        })
        .reduce(function(word,counts){
            this.emit(word, counts.length);
        })
        // runLocal can be used instead of run to simulate the job execution 
        // from the command line
        .runLocal("~/Desktop/test_input.txt");

Initialising a job

    require('timothy')
        .configure({	
             config: "./hadoop.xml",
             input:  "/test.txt",
             output: "/processed_"+(new Date().getTime()),
             name:   "Timothy Word Count Example"
        })
        // global variables and functions will be available in the map and reduce functions
        .setup(function(){
            x = 0;
            inc = function() {
                x = x + 1;
            };
        })
        .map(function(line){
            var words = line.split(" ");
            for(var i=0; i<words.length; i++) {
                inc();
                this.emit(words[i], x);
            }
        })
        .reduce(function(word,counts){
            this.emit(word, counts.length);
        })
        .run();

Passing Environment Variables

    (function(offset1,offset2){

        require('timothy')
            .configure({	
                 config: "./hadoop.xml",
                 input:  "/test.txt",
                 output: "/processed_"+(new Date().getTime()),
                 name:   "Timothy Word Count Example",
                 //environment variables
                 cmdenv: "offset1="+offset1+",offset2="+offset2 
            })
            .map(function(line){
    	        // mapper and reducer process can now access
                // the variables through process.env
                var offset1 = parseInt(process.env['offset1']);
                var words = line.split(" ");
                for(var i=0; i<words.length; i++)
                    this.emit(words[i], 1+offset1);
            })
            .reduce(function(word,counts){
                var offset2 = parseInt(process.env['offset2']);
                this.emit(word, counts.length+offset2);
            })
            .run();

    })(10,40);

Using node libraries

    require('timothy')
        .configure({	
             config: "./hadoop.xml",
             input:  "/test.txt",
             output: "/processed_"+(new Date().getTime()),
             name:   "Timothy Word Count Example"
        })
        // Libraries can be added using the same syntax as
        // in a NPM package.json file
        .dependencies({"node-uuid":"1.3.3"})
        .setup(function(){
            // libraries can be required in the setup function
            uuid = require('node-uuid');
        })
        .map(function(line){
            var words = line.split(" ");
            for(var i=0; i<words.length; i++) {
                   this.emit(words[i], 1);
            }
        })
        .reduce(function(word,counts){
            this.emit(word, counts.length);
            this.emit(uuid.v1(),"10000000");
        })
        .run();

Status and counters

Status and counters for the job can be updated using the this.updateStatus and this.updateCounter functions.

Caveats

map, reduce and setup functions are used as templates for the job functions. Trying to use values from these function definition closures will fail when running the actual job. Use the 'cmdenv' configuration to pass values to the job instead.

At the moment, the setup function does not handle blocking asynchronous operations. If one of these operations is invoked, the script will continue executing the map/reduce function before the asynchronous callback is executed.

About

Forward Internet Group (c) 2012. Available under the LGPL V3 license.

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