我有这个主...使用自定义组合器...它可能被忽略?
job.setMapperClass(AverageIntMapper.class);
job.setCombinerClass(AverageIntCombiner.class);
job.setReducerClass(AverageIntReducer.class);
与组合有不同的代码,但该组合被完全忽略的减速器使用输出从映射器输出。
我明白一个Combiner可能不会被使用,但我认为这是Combiner和Reducer一样的情况。我真的不明白能够创建自定义组合器的意义,但系统仍然可以跳过它的使用。
如果不应该发生这种情况,可能是组合器没有被使用的原因是什么?
代码...
import java.io.IOException;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.DoubleWritable;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.mapreduce.Reducer;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
public class AverageInt {
public static class AverageIntMapper extends Mapper<LongWritable, Text, Text, Text> {
public void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
String n_string = value.toString();
context.write(new Text("Value"), new Text(n_string));
}
}
public static class AverageIntCombiner extends Reducer<Text, Text, Text, Text> {
public void reduce(Text key, Iterable<IntWritable> values, Context context) throws IOException, InterruptedException {
int sum = 0;
int count = 0;
for(IntWritable value : values) {
int temp = Integer.parseInt(value.toString());
sum += value.get();
count += 1;
}
String sum_count = Integer.toString(sum) + "," + Integer.toString(count);
context.write(key, new Text(sum_count));
}
}
public static class AverageIntReducer extends Reducer<Text, Text, Text, Text> {
public void reduce(Text key, Iterable<Text> values, Context context) throws IOException, InterruptedException {
int total = 0;
int count = 0;
for(Text value : values) {
String temp = value.toString();
String[] split = temp.split(",");
total += Integer.parseInt(split[0]);
count += Integer.parseInt(split[1]);
}
Double average = (double)total/count;
context.write(key, new Text(average.toString()));
}
}
public static void main(String[] args) throws Exception {
if(args.length != 2) {
System.err.println("Usage: AverageInt <input path> <output path>");
System.exit(-1);
}
Job job = new Job();
job.setJarByClass(AverageInt.class);
job.setJobName("Average");
FileInputFormat.addInputPath(job, new Path(args[0]));
FileOutputFormat.setOutputPath(job, new Path(args[1]));
job.setMapperClass(AverageIntMapper.class);
job.setCombinerClass(AverageIntCombiner.class);
job.setReducerClass(AverageIntReducer.class);
job.setOutputKeyClass(Text.class);
job.setOutputValueClass(Text.class);
System.exit(job.waitForCompletion(true) ? 0 : 1);
}
}
你怎么知道它被忽略?组合器没有数量吗? –
@BinaryNerd在Combiner中创建的值有一个分隔符,我尝试在Reducer中分割,但当我尝试分割时,出现数组越界的错误。如果我删除了在Reducer中分割的逻辑并输出它作为输入获取的值,那么Mapper会输出这些值。 – cpd1
我会发布你的代码,否则它不可能有人能帮助你。 –