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From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] [Resolved] (HDFS-2091) Hadoop does not scale as expected
Date Tue, 21 Jun 2011 04:23:47 GMT

     [ https://issues.apache.org/jira/browse/HDFS-2091?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Todd Lipcon resolved HDFS-2091.
-------------------------------

    Resolution: Invalid

Hi Alberto. This is the bug tracker rather than a place for questions. You might try the mapreduce-user
mailing list.

> Hadoop does not scale as expected
> ---------------------------------
>
>                 Key: HDFS-2091
>                 URL: https://issues.apache.org/jira/browse/HDFS-2091
>             Project: Hadoop HDFS
>          Issue Type: Bug
>         Environment: Linux, 8 nodes.
>            Reporter: Alberto Andreotti
>   Original Estimate: 504h
>  Remaining Estimate: 504h
>
> The more nodes I add to this application, the slower it goes. This is the app's map,
>  public void map(IntWritable linearPos, FloatWritable heat, Context context
>                             ) throws IOException, InterruptedException {
>        int myLinearPos = linearPos.get();
>        //Distribute my value to the previous and the next
>        linearPos.set(myLinearPos - 1);
>        context.write(linearPos, heat);
>        linearPos.set(myLinearPos + 1);
>        context.write(linearPos, heat);
>        //Distribute my value to the cells above and below
>        linearPos.set(myLinearPos - MatrixData.Length());
>        context.write(linearPos, heat);
>        linearPos.set(myLinearPos + MatrixData.Length());
>        context.write(linearPos, heat);
>     }//end map
> and this is the reduce,
> public void reduce(IntWritable linearPos, Iterable<FloatWritable> fwValues,
>                      Context context) throws IOException, InterruptedException {
>        //Handle first and last "cold" boundaries
>        if(linearPos.get()<0 || linearPos.get()>MatrixData.LinearSize()){
>           return;
>        }
>        if(linearPos.get()==MatrixData.HeatSourceLinearPos()){
>           context.write(linearPos, new FloatWritable(MatrixData.HeatSourceTemperature()));
>           return;
>        }
>        float result = 0.0f;
>        //Add all the values
>        for(FloatWritable heat : fwValues) {
>           result += heat.get();
>        }
>       context.write(linearPos, new FloatWritable(result/4) );
> }
> For example, with 6 nodes I get a running time of 15minutes, and with 4 nodes I get a
running time of 8minutes!.
> This is how I generated the input,
>  public static void main(String[] args) throws IOException {
>      //Write file in the local dir
>      String uri = "/home/beto/mySeq";
>      Configuration conf = new Configuration();
>      FileSystem fs = FileSystem.get(URI.create(uri), conf);
>      Path path = new Path(uri);
>      IntWritable key = new IntWritable();
>      FloatWritable value = new FloatWritable(0.0f);
>      SequenceFile.Writer writer = null;
>      try {
>        writer = SequenceFile.createWriter(fs, conf, path, key.getClass(), value.getClass());
>      int step = MatrixData.LinearSize()/10;
>      int limit = step;
>      for (int i = 0; i <= MatrixData.LinearSize(); i++) {
>         key.set(i);
>         if(i>limit){
>              System.out.println("*");
>              limit +=step;
>         }
>           if(i==MatrixData.HeatSourceLinearPos()) {
>             writer.append(key, new FloatWritable(MatrixData.HeatSourceTemperature()));
>             continue;
>           }
>         writer.append(key, value);
>       }
>     } finally {
>       IOUtils.closeStream(writer);
>     }
>   }
> I'm basically solving a heat transfer problem in a squared section. Pretty simple. The
input data is being stored as a (key, value) pairs, read in this way, processed, and written
again in the same format.
> Any thoughts?
> Alberto.

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