Hadoop MapReduce 学习笔记(九) MapReduce实现类似SQL的order by/排序 正确写法
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?????? 请先阅读:??????????
?????????? 1.Hadoop MapReduce 学习笔记(一) 序言和准备
?????????? 2.Hadoop MapReduce 学习笔记(二) 序言和准备 2
??????????????? 3.Hadoop MapReduce 学习笔记(八) MapReduce实现类似SQL的order by/排序
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????? Hadoop MapReduce 学习笔记(八) MapReduce实现类似SQL的order by/排序写法会触发内存溢出,因为将数据都放到一个内存容器中.这是我一开始所想到的,后来触发了OOM.于是想到了借用map输出的自己的排序,网上找资料以及hadoop/examples下也是这种写法.代码如下:
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package com.guoyun.hadoop.mapreduce.study;import java.io.IOException;import org.apache.hadoop.conf.Configuration;import org.apache.hadoop.fs.FileSystem;import org.apache.hadoop.fs.Path;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;import org.slf4j.Logger;import org.slf4j.LoggerFactory;/** * 对具有多列数据中的一列进行从小到大排序，并返回结果 * 如果想实现从大到小，或者多列数据排序,请自己实现 @WritableComparable * 需要实现对多列排序，例如SQL： * SELECT ＊ FROM TABLE ORDER BY COL1 ASC，COL2 ASC 请查看 ＠OrderByMultiMapReduceTest */public class OrderBySingleMapReduceFixTest extends MyMapReduceMultiColumnTest { public static final Logger log=LoggerFactory.getLogger(OrderBySingleMapReduceFixTest.class); public OrderBySingleMapReduceFixTest(long dataLength) throws Exception { super(dataLength); // TODO Auto-generated constructor stub } public OrderBySingleMapReduceFixTest(String outputPath) throws Exception { super(outputPath); // TODO Auto-generated constructor stub } public OrderBySingleMapReduceFixTest(long dataLength, String inputPath, String outputPath) throws Exception { super(dataLength, inputPath, outputPath); // TODO Auto-generated constructor stub } /** * Map,to get the source datas */ private static class MyMapper extends Mapper<LongWritable,Text,LongWritable,Text>{ private final LongWritable writeKey=new LongWritable(0); private Text writeValue=new Text(); @Override protected void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException { log.debug("begin to map"); String[] splits=null; try { splits=value.toString().split("\\t"); if(splits!=null&&splits.length==2){ writeValue.set(splits[0]); writeKey.set(Long.parseLong(splits[1].trim())); } } catch (NumberFormatException e) { log.error("map error:"+e.getMessage()); } context.write(writeKey, writeValue); } } private static class MyReducer extends Reducer<LongWritable,Text,LongWritable,Text>{ @Override protected void reduce(LongWritable key, Iterable<Text> values, Context context) throws IOException, InterruptedException { for(Text value:values){ context.write(key, value); } } } /** * @param args */ public static void main(String[] args) { MyMapReduceTest mapReduceTest=null; Configuration conf=null; Job job=null; FileSystem fs=null; Path inputPath=null; Path outputPath=null; long begin=0; String input="testDatas/mapreduce/MRInput_Single_OrderBy_Fix"; String output="testDatas/mapreduce/MROutput_Single_OrderBy_Fix"; try { mapReduceTest=new OrderBySingleMapReduceFixTest(100000,input,output); inputPath=new Path(mapReduceTest.getInputPath()); outputPath=new Path(mapReduceTest.getOutputPath()); conf=new Configuration(); job=new Job(conf,"OrderBy"); fs=FileSystem.getLocal(conf); if(fs.exists(outputPath)){ if(!fs.delete(outputPath,true)){ System.err.println("Delete output file:"+mapReduceTest.getOutputPath()+" failed!"); return; } } job.setJarByClass(OrderBySingleMapReduceFixTest.class); job.setMapOutputKeyClass(LongWritable.class); job.setMapOutputValueClass(Text.class); job.setOutputKeyClass(LongWritable.class); job.setOutputValueClass(Text.class); job.setMapperClass(MyMapper.class); job.setReducerClass(MyReducer.class); job.setNumReduceTasks(2); FileInputFormat.addInputPath(job, inputPath); FileOutputFormat.setOutputPath(job, outputPath); begin=System.currentTimeMillis(); job.waitForCompletion(true); System.out.println("==================================================="); if(mapReduceTest.isGenerateDatas()){ System.out.println("The maxValue is:"+mapReduceTest.getMaxValue()); System.out.println("The minValue is:"+mapReduceTest.getMinValue()); } System.out.println("Spend time:"+(System.currentTimeMillis()-begin)); // Spend time:13361 } catch (Exception e) { // TODO Auto-generated catch block e.printStackTrace(); } }}