mapreduce實現全局排序

jopen 11年前發布 | 36K 次閱讀 MapReduce

直接附代碼，說明都在源碼里了。

package com.hadoop.totalsort;

import java.io.IOException;
import java.util.ArrayList;

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.NullWritable;
import org.apache.hadoop.io.SequenceFile;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapred.FileInputFormat;
import org.apache.hadoop.mapred.FileSplit;
import org.apache.hadoop.mapred.InputSplit;
import org.apache.hadoop.mapred.JobConf;
import org.apache.hadoop.mapred.LineRecordReader;
import org.apache.hadoop.mapred.RecordReader;
import org.apache.hadoop.mapred.Reporter;
import org.apache.hadoop.util.IndexedSortable;
import org.apache.hadoop.util.QuickSort;


public class SamplerInputFormat extends FileInputFormat<Text, Text> {  

    static final String PARTITION_FILENAME = "_partition.lst";  
    static final String SAMPLE_SIZE = "terasort.partitions.sample";  
    private static JobConf lastConf = null;  
    private static InputSplit[] lastResult = null;  

    static class TextSampler implements IndexedSortable {  

        public ArrayList<Text> records = new ArrayList<Text>();  

        public int compare(int arg0, int arg1) {  
            Text right = records.get(arg0);  
            Text left = records.get(arg1);  

            return right.compareTo(left);  
        }  

        public void swap(int arg0, int arg1) {  
            Text right = records.get(arg0);  
            Text left = records.get(arg1);  

            records.set(arg0, left);  
            records.set(arg1, right);  
        }  

        public void addKey(Text key) {  
            records.add(new Text(key));  
        }  


        //將采集出來的key數據排序
        public Text[] createPartitions(int numPartitions) {  
            int numRecords = records.size();  
            if (numPartitions > numRecords) {  
                throw new IllegalArgumentException("Requested more partitions than input keys (" + numPartitions +  
                        " > " + numRecords + ")");  
            }  
            new QuickSort().sort(this, 0, records.size());  
            float stepSize = numRecords / (float) numPartitions;  //采集的時候應該是采了100條記錄,從10個分片查找的,此處再取numPartitions-1條
            Text[] result = new Text[numPartitions - 1];  
            for (int i = 1; i < numPartitions; ++i) {  
                result[i - 1] = records.get(Math.round(stepSize * i));  
            }  
            return result;  
        }  

    }  

    public static void writePartitionFile(JobConf conf, Path partFile) throws IOException {  
        //前段代碼從分片中采集數據，通過sampler.addKey存入TextSampler中的records數組
        SamplerInputFormat inputFormat = new SamplerInputFormat();  
        TextSampler sampler = new TextSampler();  
        Text key = new Text();  
        Text value = new Text();  

        int partitions = conf.getNumReduceTasks(); // Reducer任務的個數   
        long sampleSize = conf.getLong(SAMPLE_SIZE, 100); // 采集數據-鍵值對的個數   
        InputSplit[] splits = inputFormat.getSplits(conf, conf.getNumMapTasks());// 獲得數據分片   
        int samples = Math.min(10, splits.length);// 采集分片的個數   ,采集10個分片
        long recordsPerSample = sampleSize / samples;// 每個分片采集的鍵值對個數   
        int sampleStep = splits.length / samples; // 采集分片的步長   ,總的分片個數/要采集的分片個數
        long records = 0;  

        for (int i = 0; i < samples; i++) {  //1...10分片數
            RecordReader<Text, Text> reader = inputFormat.getRecordReader(splits[sampleStep * i], conf, null);  
            while (reader.next(key, value)) {  
                sampler.addKey(key);   //將key值增加到sampler的records數組
                records += 1;  
                if ((i + 1) * recordsPerSample <= records) {  //目的是均勻采集各分片的條數，比如采集到第5個分片,那么記錄條數應該小于5個分片應該的條數
                    break;  
                }  
            }  
        }  
        FileSystem outFs = partFile.getFileSystem(conf);  
        if (outFs.exists(partFile)) {  
            outFs.delete(partFile, false);  
        }  
        SequenceFile.Writer writer = SequenceFile.createWriter(outFs, conf, partFile, Text.class, NullWritable.class);  
        NullWritable nullValue = NullWritable.get();  
        for (Text split : sampler.createPartitions(partitions)) {  //調用createPartitions方法，排序采集出來的數據，并取partitions條
            writer.append(split, nullValue);  
        }  
        writer.close();  

    }  

    static class TeraRecordReader implements RecordReader<Text, Text> {  

        private LineRecordReader in;  
        private LongWritable junk = new LongWritable();  
        private Text line = new Text();  
        private static int KEY_LENGTH = 10;  

        public TeraRecordReader(Configuration job, FileSplit split) throws IOException {  
            in = new LineRecordReader(job, split);  
        }  

        public void close() throws IOException {  
            in.close();  
        }  

        public Text createKey() {  
            // TODO Auto-generated method stub   
            return new Text();  
        }  

        public Text createValue() {  
            return new Text();  
        }  

        public long getPos() throws IOException {  
            // TODO Auto-generated method stub   
            return in.getPos();  
        }  

        public float getProgress() throws IOException {  
            // TODO Auto-generated method stub   
            return in.getProgress();  
        }  

        public boolean next(Text arg0, Text arg1) throws IOException {  
            if (in.next(junk, line)) {   //調用父類方法,將value值賦給key
               // if (line.getLength() < KEY_LENGTH) {   
                    arg0.set(line);  
                    arg1.clear();  
//                } else {   
//                    byte[] bytes = line.getBytes(); // 默認知道讀取要比較值的前10個字節 作為key   
//                                                    // 后面的字節作為value；   
//                    arg0.set(bytes, 0, KEY_LENGTH);   
//                    arg1.set(bytes, KEY_LENGTH, line.getLength() - KEY_LENGTH);   
//                }   
                return true;  
            } else {  
                return false;  
            }  
        }  

    }  

    @Override  
    public InputSplit[] getSplits(JobConf conf, int splits) throws IOException {  
        if (conf == lastConf) {  
            return lastResult;  
        }  
        lastConf = conf;  
        lastResult = super.getSplits(lastConf, splits);  
        return lastResult;  

    }  

    public org.apache.hadoop.mapred.RecordReader<Text, Text> getRecordReader(InputSplit arg0, JobConf arg1,  
            Reporter arg2) throws IOException {  
        return new TeraRecordReader(arg1, (FileSplit) arg0);  
    }  

}

package com.hadoop.totalsort;

import java.io.IOException;
import java.net.URI;
import java.util.ArrayList;
import java.util.List;

import org.apache.hadoop.conf.Configured;
import org.apache.hadoop.filecache.DistributedCache;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.NullWritable;
import org.apache.hadoop.io.SequenceFile;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapred.FileOutputFormat;
import org.apache.hadoop.mapred.JobClient;
import org.apache.hadoop.mapred.JobConf;
import org.apache.hadoop.mapred.Partitioner;
import org.apache.hadoop.mapred.TextOutputFormat;
import org.apache.hadoop.util.Tool;
import org.apache.hadoop.util.ToolRunner;

public class SamplerSort extends Configured implements Tool {  

    // 自定義的Partitioner   
    public static class TotalOrderPartitioner implements Partitioner<Text, Text> {  

        private Text[] splitPoints;  

        public TotalOrderPartitioner() {  
        }  

        public int getPartition(Text arg0, Text arg1, int arg2) {  
            // TODO Auto-generated method stub   
            return findPartition(arg0);  
        }  

        public void configure(JobConf arg0) {  
            try {  
                FileSystem fs = FileSystem.getLocal(arg0);  
                Path partFile = new Path(SamplerInputFormat.PARTITION_FILENAME);  
                splitPoints = readPartitions(fs, partFile, arg0); // 讀取采集文件   
            } catch (IOException ie) {  
                throw new IllegalArgumentException("can't read paritions file", ie);  
            }  

        }  

        public int findPartition(Text key) // 分配可以到多個reduce   
        {  
            int len = splitPoints.length;  
            for (int i = 0; i < len; i++) {  
                int res = key.compareTo(splitPoints[i]);  
                if (res > 0 && i < len - 1) {  
                    continue;  
                } else if (res == 0) {  
                    return i;  
                } else if (res < 0) {  
                    return i;  
                } else if (res > 0 && i == len - 1) {  
                    return i + 1;  
                }  
            }  
            return 0;  
        }  

        private static Text[] readPartitions(FileSystem fs, Path p, JobConf job) throws IOException {  
            SequenceFile.Reader reader = new SequenceFile.Reader(fs, p, job);  
            List<Text> parts = new ArrayList<Text>();  
            Text key = new Text();  
            NullWritable value = NullWritable.get();  
            while (reader.next(key, value)) {  
                parts.add(key);  
            }  
            reader.close();  
            return parts.toArray(new Text[parts.size()]);  
        }  

    }  

    public int run(String[] args) throws Exception {  
        JobConf job = (JobConf) getConf();  
       // job.set(name, value);   
        Path inputDir = new Path(args[0]);  
        inputDir = inputDir.makeQualified(inputDir.getFileSystem(job));  
        Path partitionFile = new Path(inputDir, SamplerInputFormat.PARTITION_FILENAME);  

        URI partitionUri = new URI(partitionFile.toString() +  
                "#" + SamplerInputFormat.PARTITION_FILENAME);  

        SamplerInputFormat.setInputPaths(job, new Path(args[0]));  
        FileOutputFormat.setOutputPath(job, new Path(args[1]));  

        job.setJobName("SamplerTotalSort");  
        job.setJarByClass(SamplerSort.class);  
        job.setOutputKeyClass(Text.class);  
        job.setOutputValueClass(Text.class);  
        job.setInputFormat(SamplerInputFormat.class);  
        job.setOutputFormat(TextOutputFormat.class);  
        job.setPartitionerClass(TotalOrderPartitioner.class);  
        job.setNumReduceTasks(4);  

        SamplerInputFormat.writePartitionFile(job, partitionFile); // 數據采集并寫入文件   

        DistributedCache.addCacheFile(partitionUri, job); // 將這個文件作為共享文件   
        DistributedCache.createSymlink(job);  
        // SamplerInputFormat.setFinalSync(job, true);   
        JobClient.runJob(job);  
        return 0;  
    }  

    public static void main(String[] args) throws Exception {  
        int res = ToolRunner.run(new JobConf(), new SamplerSort(), args);  
        System.exit(res);  
    }  

}

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mapreduce實現全局排序

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