hadoop之数据倾斜

数据倾斜

1.产生原因   大量的key进入到了一个或者是少数的几个reduce.

2.解决办法：

  　　1.重新设计key；

     2.设计分区类    随机分区 (常用）；

     3.自定义Shuffle机制。   

实例：

  1 import org.apache.hadoop.conf.Configuration;
  2 import org.apache.hadoop.fs.Path;
  3 import org.apache.hadoop.io.IntWritable;
  4 import org.apache.hadoop.io.Text;
  5 import org.apache.hadoop.mapreduce.Job;
  6 import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
  7 import org.apache.hadoop.mapreduce.lib.input.KeyValueTextInputFormat;
  8 import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
  9 
 10 /**
 11  * Created by Administrator on 2017/6/1.
 12  */
 13 public class App {
 14     public static void main(String[] args) throws Exception {
 15         Configuration conf = new Configuration();
 16         conf.set("fs.defaultFS", "file:///");
 17         conf.set("mapreduce.framework.name", "local");
 18         Job job = Job.getInstance(conf);
 19         job.setJobName("WordCount");
 20         job.setJarByClass(App.class);
 21 
 22         FileInputFormat.addInputPath(job, new Path("d:/mr/wc.txt"));
 23         FileOutputFormat.setOutputPath(job, new Path("d:/mr/out"));
 24         
 25         job.setMapperClass(WordCountMapper.class);
 26         job.setReducerClass(WordCountReducer.class);
 27         
 28         job.setNumReduceTasks(3);
 29 
 30         //设置输出kv类型
 31         job.setOutputKeyClass(Text.class);
 32         job.setOutputValueClass(IntWritable.class);
 33 
 34         //设置分区类
 35         job.setPartitionerClass(RandomPartitioner.class);
 36         boolean b = job.waitForCompletion(true);
 37         //进行二次job
 38         if(b){
 39             conf = new Configuration();
 40             conf.set("fs.defaultFS", "file:///");
 41             conf.set("mapreduce.framework.name", "local");
 42             job = Job.getInstance(conf);
 43             job.setJobName("WordCount2");
 44             job.setJarByClass(App.class);
 45             FileInputFormat.addInputPath(job, new Path("d:/mr/out/part-r*"));
 46             FileOutputFormat.setOutputPath(job, new Path("d:/mr/out2"));
 47 
 48             job.setInputFormatClass(KeyValueTextInputFormat.class);
 49 
 50             job.setMapperClass(WordCountMapper2.class);
 51             job.setReducerClass(WordCountReducer.class);
 52 
 53             job.setNumReduceTasks(3);
 54 
 55             //设置输出kv类型
 56             job.setOutputKeyClass(Text.class);
 57             job.setOutputValueClass(IntWritable.class);
 58             job.waitForCompletion(true);
 59         }
 60     }
 61 }
 62 
 63 
 64 import org.apache.hadoop.io.IntWritable;
 65 import org.apache.hadoop.io.LongWritable;
 66 import org.apache.hadoop.io.Text;
 67 import org.apache.hadoop.mapreduce.Mapper;
 68 
 69 import java.io.IOException;
 70 
 71 /**
 72  * 创建Mapper
 73  */
 74 public class WordCountMapper extends Mapper<LongWritable,Text,Text,IntWritable> {
 75     protected void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
 76         String[] arr = value.toString().split(" ");
 77         for(String word : arr){
 78             context.write(new Text(word),new IntWritable(1));
 79         }
 80     }
 81 }
 82 
 83 
 84 
 85 import org.apache.hadoop.io.IntWritable;
 86 import org.apache.hadoop.io.LongWritable;
 87 import org.apache.hadoop.io.Text;
 88 import org.apache.hadoop.mapreduce.Mapper;
 89 
 90 import java.io.IOException;
 91 
 92 /**
 93  * 创建Mapper2
 94  */
 95 public class WordCountMapper2 extends Mapper<Text,Text,Text,IntWritable> {
 96     protected void map(Text key, Text value, Context context) throws IOException, InterruptedException {
 97         context.write(key,new IntWritable(Integer.parseInt(value.toString())));
 98     }
 99 }
100 
101 
102 
103 import org.apache.hadoop.io.IntWritable;
104 import org.apache.hadoop.io.LongWritable;
105 import org.apache.hadoop.io.Text;
106 import org.apache.hadoop.mapreduce.Reducer;
107 
108 import java.io.IOException;
109 
110 /**
111  * Reducer
112  */
113 public class WordCountReducer extends Reducer<Text, IntWritable,Text,IntWritable> {
114     protected void reduce(Text key, Iterable<IntWritable> values, Context context) throws IOException, InterruptedException {
115         int count = 0 ;
116         for(IntWritable iw : values){
117             count = count + iw.get();
118         }
119         context.write(key,new IntWritable(count));
120     }
121 }
122 
123 
124 import org.apache.hadoop.io.IntWritable;
125 import org.apache.hadoop.io.Text;
126 import org.apache.hadoop.mapreduce.Partitioner;
127 
128 import java.util.Random;
129 
130 /**
131  * Created by Administrator on 2017/6/1.
132  */
133 public class RandomPartitioner extends Partitioner<Text,IntWritable>{
134     Random r = new Random();
135     public int getPartition(Text text, IntWritable intWritable, int numPartitions) {
136         return r.nextInt(numPartitions);
137     }
138 }

 

posted on 2017-06-02 01:39  艺海浮台  阅读(197)  评论(0)  编辑  收藏  举报