Java tutorial
/** * Licensed to the Apache Software Foundation (ASF) under one * or more contributor license agreements. See the NOTICE file * distributed with this work for additional information * regarding copyright ownership. The ASF licenses this file * to you under the Apache License, Version 2.0 (the * "License"); you may not use this file except in compliance * with the License. You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package org.apache.hadoop.examples.terasort; import java.io.DataOutputStream; import java.io.EOFException; import java.io.IOException; import java.util.ArrayList; import java.util.List; import org.apache.hadoop.conf.Configuration; import org.apache.hadoop.fs.FSDataInputStream; import org.apache.hadoop.fs.FileSystem; import org.apache.hadoop.fs.Path; import org.apache.hadoop.io.Text; import org.apache.hadoop.mapreduce.InputSplit; import org.apache.hadoop.mapreduce.JobContext; import org.apache.hadoop.mapreduce.MRJobConfig; import org.apache.hadoop.mapreduce.RecordReader; import org.apache.hadoop.mapreduce.TaskAttemptContext; import org.apache.hadoop.mapreduce.TaskAttemptID; import org.apache.hadoop.mapreduce.lib.input.FileInputFormat; import org.apache.hadoop.mapreduce.lib.input.FileSplit; import org.apache.hadoop.mapreduce.task.TaskAttemptContextImpl; import org.apache.hadoop.util.IndexedSortable; import org.apache.hadoop.util.QuickSort; import org.apache.hadoop.util.StringUtils; /** * An input format that reads the first 10 characters of each line as the key * and the rest of the line as the value. Both key and value are represented * as Text. */ public class TeraInputFormat extends FileInputFormat<Text, Text> { static final String PARTITION_FILENAME = "_partition.lst"; static final int KEY_LENGTH = 10; static final int VALUE_LENGTH = 90; static final int RECORD_LENGTH = KEY_LENGTH + VALUE_LENGTH; private static MRJobConfig lastContext = null; private static List<InputSplit> lastResult = null; static class TextSampler implements IndexedSortable { private ArrayList<Text> records = new ArrayList<Text>(); public int compare(int i, int j) { Text left = records.get(i); Text right = records.get(j); return left.compareTo(right); } public void swap(int i, int j) { Text left = records.get(i); Text right = records.get(j); records.set(j, left); records.set(i, right); } public void addKey(Text key) { synchronized (this) { records.add(new Text(key)); } } /** * Find the split points for a given sample. The sample keys are sorted * and down sampled to find even split points for the partitions. The * returned keys should be the start of their respective partitions. * @param numPartitions the desired number of partitions * @return an array of size numPartitions - 1 that holds the split points */ Text[] createPartitions(int numPartitions) { int numRecords = records.size(); System.out.println("Making " + numPartitions + " from " + numRecords + " sampled records"); 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; Text[] result = new Text[numPartitions - 1]; for (int i = 1; i < numPartitions; ++i) { result[i - 1] = records.get(Math.round(stepSize * i)); } return result; } } /** * Use the input splits to take samples of the input and generate sample * keys. By default reads 100,000 keys from 10 locations in the input, sorts * them and picks N-1 keys to generate N equally sized partitions. * @param job the job to sample * @param partFile where to write the output file to * @throws Throwable if something goes wrong */ public static void writePartitionFile(final JobContext job, Path partFile) throws Throwable { long t1 = System.currentTimeMillis(); Configuration conf = job.getConfiguration(); final TeraInputFormat inFormat = new TeraInputFormat(); final TextSampler sampler = new TextSampler(); int partitions = job.getNumReduceTasks(); long sampleSize = conf.getLong(TeraSortConfigKeys.SAMPLE_SIZE.key(), TeraSortConfigKeys.DEFAULT_SAMPLE_SIZE); final List<InputSplit> splits = inFormat.getSplits(job); long t2 = System.currentTimeMillis(); System.out.println("Computing input splits took " + (t2 - t1) + "ms"); int samples = Math.min( conf.getInt(TeraSortConfigKeys.NUM_PARTITIONS.key(), TeraSortConfigKeys.DEFAULT_NUM_PARTITIONS), splits.size()); System.out.println("Sampling " + samples + " splits of " + splits.size()); final long recordsPerSample = sampleSize / samples; final int sampleStep = splits.size() / samples; Thread[] samplerReader = new Thread[samples]; SamplerThreadGroup threadGroup = new SamplerThreadGroup("Sampler Reader Thread Group"); // take N samples from different parts of the input for (int i = 0; i < samples; ++i) { final int idx = i; samplerReader[i] = new Thread(threadGroup, "Sampler Reader " + idx) { { setDaemon(true); } public void run() { long records = 0; try { TaskAttemptContext context = new TaskAttemptContextImpl(job.getConfiguration(), new TaskAttemptID()); RecordReader<Text, Text> reader = inFormat.createRecordReader(splits.get(sampleStep * idx), context); reader.initialize(splits.get(sampleStep * idx), context); while (reader.nextKeyValue()) { sampler.addKey(new Text(reader.getCurrentKey())); records += 1; if (recordsPerSample <= records) { break; } } } catch (IOException ie) { System.err.println( "Got an exception while reading splits " + StringUtils.stringifyException(ie)); throw new RuntimeException(ie); } catch (InterruptedException e) { } } }; samplerReader[i].start(); } FileSystem outFs = partFile.getFileSystem(conf); DataOutputStream writer = outFs.create(partFile, true, 64 * 1024, (short) 10, outFs.getDefaultBlockSize(partFile)); for (int i = 0; i < samples; i++) { try { samplerReader[i].join(); if (threadGroup.getThrowable() != null) { throw threadGroup.getThrowable(); } } catch (InterruptedException e) { } } for (Text split : sampler.createPartitions(partitions)) { split.write(writer); } writer.close(); long t3 = System.currentTimeMillis(); System.out.println("Computing parititions took " + (t3 - t2) + "ms"); } static class SamplerThreadGroup extends ThreadGroup { private Throwable throwable; public SamplerThreadGroup(String s) { super(s); } @Override public void uncaughtException(Thread thread, Throwable throwable) { this.throwable = throwable; } public Throwable getThrowable() { return this.throwable; } } static class TeraRecordReader extends RecordReader<Text, Text> { private FSDataInputStream in; private long offset; private long length; private static final int RECORD_LENGTH = KEY_LENGTH + VALUE_LENGTH; private byte[] buffer = new byte[RECORD_LENGTH]; private Text key; private Text value; public TeraRecordReader() throws IOException { } public void initialize(InputSplit split, TaskAttemptContext context) throws IOException, InterruptedException { Path p = ((FileSplit) split).getPath(); FileSystem fs = p.getFileSystem(context.getConfiguration()); in = fs.open(p); long start = ((FileSplit) split).getStart(); // find the offset to start at a record boundary offset = (RECORD_LENGTH - (start % RECORD_LENGTH)) % RECORD_LENGTH; in.seek(start + offset); length = ((FileSplit) split).getLength(); } public void close() throws IOException { in.close(); } public Text getCurrentKey() { return key; } public Text getCurrentValue() { return value; } public float getProgress() throws IOException { return (float) offset / length; } public boolean nextKeyValue() throws IOException { if (offset >= length) { return false; } int read = 0; while (read < RECORD_LENGTH) { long newRead = in.read(buffer, read, RECORD_LENGTH - read); if (newRead == -1) { if (read == 0) { return false; } else { throw new EOFException("read past eof"); } } read += newRead; } if (key == null) { key = new Text(); } if (value == null) { value = new Text(); } key.set(buffer, 0, KEY_LENGTH); value.set(buffer, KEY_LENGTH, VALUE_LENGTH); offset += RECORD_LENGTH; return true; } } @Override public RecordReader<Text, Text> createRecordReader(InputSplit split, TaskAttemptContext context) throws IOException { return new TeraRecordReader(); } @Override public List<InputSplit> getSplits(JobContext job) throws IOException { if (job == lastContext) { return lastResult; } long t1, t2, t3; t1 = System.currentTimeMillis(); lastContext = job; lastResult = super.getSplits(job); t2 = System.currentTimeMillis(); System.out.println("Spent " + (t2 - t1) + "ms computing base-splits."); if (job.getConfiguration().getBoolean(TeraSortConfigKeys.USE_TERA_SCHEDULER.key(), TeraSortConfigKeys.DEFAULT_USE_TERA_SCHEDULER)) { TeraScheduler scheduler = new TeraScheduler(lastResult.toArray(new FileSplit[0]), job.getConfiguration()); lastResult = scheduler.getNewFileSplits(); t3 = System.currentTimeMillis(); System.out.println("Spent " + (t3 - t2) + "ms computing TeraScheduler splits."); } return lastResult; } }