琐碎-hadoop1.X和2.X的区别

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1.  jobtracker做了分离，分成了resourceManager和nodemanager；

2.  MR变成了和HBase和Hive等一样的yarn上面的一个应用；

3.  1.x的默认块大小为64M，2.x的默认块大小为128M；

4.  在2.x中除了datanode要向namenode报告status，nodemanager也要向ResourceManager报告status

5. MR API差别

旧的WordCount

package org.apache.hadoop.mapred;

... ...

public class WordCount extends Configured implements Tool {
  
  public static class MapClass extends MapReduceBase
    implements Mapper<LongWritable, Text, Text, IntWritable> {
    
    ... ...
    
    public void map(LongWritable key, Text value, 
                    OutputCollector<Text, IntWritable> output, 
                    Reporter reporter) throws IOException {
      ... ...
    }
  }

  public static class Reduce extends MapReduceBase
    implements Reducer<Text, IntWritable, Text, IntWritable> {
    
    public void reduce(Text key, Iterator<IntWritable> values,
                       OutputCollector<Text, IntWritable> output, 
                       Reporter reporter) throws IOException {
     ... ...
    }
  }
  
  static int printUsage() {
    System.out.println("wordcount [-m <maps>] [-r <reduces>] <input> <output>");
    ToolRunner.printGenericCommandUsage(System.out);
    return -1;
  }
   
  public int run(String[] args) throws Exception {
    ... ...
    return 0;
  }
  public static void main(String[] args) throws Exception {
    int res = ToolRunner.run(new Configuration(), new WordCount(), args);
    System.exit(res);
  }

}

新的WordCount

package org.apache.hadoop.examples;

... ...

public class WordCount {

  public static class TokenizerMapper 
       extends Mapper<Object, Text, Text, IntWritable>{
    
    ... ... 
      
    public void map(Object key, Text value, Context context
                    ) throws IOException, InterruptedException {
      ... ...
    }
  }
  
  public static class IntSumReducer 
       extends Reducer<Text,IntWritable,Text,IntWritable> {
    private IntWritable result = new IntWritable();

    public void reduce(Text key, Iterable<IntWritable> values, 
                       Context context
                       ) throws IOException, InterruptedException {
      ... ...
    }
  }

  public static void main(String[] args) throws Exception {
    ... ...
    System.exit(job.waitForCompletion(true) ? 0 : 1);
  }
}

6.

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