这可能看起来像一个愚蠢的问题,但我没有在我的mapreduce代码中看到我的类型中的问题为hadoop
正如问题中所述,问题是它期望IntWritable,但我在reducer的collector.collect中传递了一个Text对象.
我的作业配置有以下映射器输出类:
- conf.setMapOutputKeyClass(IntWritable.class);
- conf.setMapOutputValueClass(IntWritable.class);
以下减速机输出类:
- conf.setOutputKeyClass(Text.class);
- conf.setOutputValueClass(IntWritable.class);
我的映射类具有以下定义:
- public static class Reduce extends MapReduceBase implements Reducer<IntWritable,IntWritable,Text,IntWritable>
具有所需功能:
- public void reduce(IntWritable key,Iterator<IntWritable> values,OutputCollector<Text,IntWritable> output,Reporter reporter)
然后当我打电话时失败:
- output.collect(new Text(),new IntWritable());
我是相当新的map reduce,但所有类型似乎都匹配,它编译但是然后在该行上失败,说它期望IntWritable作为reduce类的键.如果重要的话我使用的是0.21版本的Hadoop
这是我的地图类:
- public static class Map extends MapReduceBase implements Mapper<LongWritable,IntWritable> {
- private IntWritable node = new IntWritable();
- private IntWritable edge = new IntWritable();
- public void map(LongWritable key,Text value,OutputCollector<IntWritable,Reporter reporter) throws IOException {
- String line = value.toString();
- StringTokenizer tokenizer = new StringTokenizer(line);
- while (tokenizer.hasMoreTokens()) {
- node.set(Integer.parseInt(tokenizer.nextToken()));
- edge.set(Integer.parseInt(tokenizer.nextToken()));
- if(node.get() < edge.get())
- output.collect(node,edge);
- }
- }
- }
和我的减少类:
- public static class Reduce extends MapReduceBase implements Reducer<IntWritable,IntWritable> {
- IntWritable $= new IntWritable(Integer.MAX_VALUE);
- Text keyText = new Text();
- public void reduce(IntWritable key,Reporter reporter) throws IOException {
- ArrayList<IntWritable> valueList = new ArrayList<IntWritable>();
- //outputs original edge pair as key and $for value
- while (values.hasNext()) {
- IntWritable value = values.next();
- valueList.add(value);
- keyText.set(key.get() + "," + value.get());
- output.collect(keyText,$);
- }
- //outputs all the 2 length pairs
- for(int i = 0; i < valueList.size(); i++)
- for(int j = i+1; i < valueList.size(); j++)
- output.collect(new Text(valueList.get(i).get() + "," + valueList.get(j).get()),key);
- }
- }
和我的工作配置:
- JobConf conf = new JobConf(Triangles.class);
- conf.setJobName("mapred1");
- conf.setMapOutputKeyClass(IntWritable.class);
- conf.setMapOutputValueClass(IntWritable.class);
- conf.setOutputKeyClass(Text.class);
- conf.setOutputValueClass(IntWritable.class);
- conf.setMapperClass(Map.class);
- conf.setCombinerClass(Reduce.class);
- conf.setReducerClass(Reduce.class);
- conf.setInputFormat(TextInputFormat.class);
- conf.setOutputFormat(TextOutputFormat.class);
- FileInputFormat.setInputPaths(conf,new Path(args[0]));
- FileOutputFormat.setOutputPath(conf,new Path("mapred1"));
- JobClient.runJob(conf);
解决方法
您的问题是您将Reduce类设置为组合器
- conf.setCombinerClass(Reduce.class);
组合器在映射阶段运行,它们需要发出相同的键/值类型(在您的情况下为IntWriteable,IntWritable)删除这一行,你应该没问题