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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

1 package org.apache.hadoop.mapred; 2  3 ... ... 4  5 public class WordCount extends Configured implements Tool { 6    7   public static class MapClass extends MapReduceBase 8     implements Mapper
     
       { 9     10     ... ...11     12     public void map(LongWritable key, Text value, 13                     OutputCollector
      
        output, 14                     Reporter reporter) throws IOException {15       ... ...16     }17   }18 19   public static class Reduce extends MapReduceBase20     implements Reducer
       
         {21     22     public void reduce(Text key, Iterator
        
          values,23                        OutputCollector
         
           output, 24                        Reporter reporter) throws IOException {25      ... ...26     }27   }28   29   static int printUsage() {30     System.out.println("wordcount [-m 
          
           ] [-r 
           
            ] 
             
            
");31 ToolRunner.printGenericCommandUsage(System.out);32 return -1;33 }34 35 public int run(String[] args) throws Exception {36 ... ...37 return 0;38 }39 public static void main(String[] args) throws Exception {40 int res = ToolRunner.run(new Configuration(), new WordCount(), args);41 System.exit(res);42 }43 44 }
           
          
         
        
       
      
     

新的WordCount

1 package org.apache.hadoop.examples; 2  3 ... ... 4  5 public class WordCount { 6  7   public static class TokenizerMapper  8        extends Mapper
     
      { 9     10     ... ... 11       12     public void map(Object key, Text value, Context context13                     ) throws IOException, InterruptedException {14       ... ...15     }16   }17   18   public static class IntSumReducer 19        extends Reducer
      
        {20     private IntWritable result = new IntWritable();21 22     public void reduce(Text key, Iterable
       
         values, 23                        Context context24                        ) throws IOException, InterruptedException {25       ... ...26     }27   }28 29   public static void main(String[] args) throws Exception {30     ... ...31     System.exit(job.waitForCompletion(true) ? 0 : 1);32   }33 }
       
      
     

6.

 

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