hadoop 取消sort
时间: 2023-06-29 14:16:59 浏览: 55
在Hadoop中,如果要取消排序,可以在MapReduce程序中使用以下方法:
1. 在Mapper中,将键设置为NullWritable,并且不输出任何键值对。
2. 在Reducer中,将输出键设置为NullWritable,并且不进行排序操作。
例如,在Mapper中可以这样写:
```
public class MyMapper extends Mapper<LongWritable, Text, NullWritable, Text> {
private Text outputValue = new Text();
@Override
protected void map(LongWritable key, Text value, Context context)
throws IOException, InterruptedException {
// do some processing on the input value
// ...
// emit the output value with a null key
outputValue.set(...);
context.write(NullWritable.get(), outputValue);
}
}
```
在Reducer中可以这样写:
```
public class MyReducer extends Reducer<NullWritable, Text, NullWritable, Text> {
private Text outputValue = new Text();
@Override
protected void reduce(NullWritable key, Iterable<Text> values, Context context)
throws IOException, InterruptedException {
// do some processing on the input values
// ...
// emit the output value with a null key
outputValue.set(...);
context.write(NullWritable.get(), outputValue);
}
}
```
这样就可以在MapReduce程序中取消排序操作。