/**
* 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.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;
/**
* 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 String SAMPLE_SIZE = "terasort.partitions.sample";
private static JobConf lastConf = null;
private static 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) {
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 +
" 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;
System.out.println("Step size is " + stepSize);
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 conf the job to sample
* @param partFile where to write the output file to
* @throws IOException if something goes wrong
*/
public static void writePartitionFile(JobConf conf,
Path partFile) throws IOException {
TeraInputFormat inFormat = new TeraInputFormat();
TextSampler sampler = new TextSampler();
Text key = new Text();
Text value = new Text();
int partitions = conf.getNumReduceTasks();
long sampleSize = conf.getLong(SAMPLE_SIZE, 100000);
InputSplit[] splits = inFormat.getSplits(conf, conf.getNumMapTasks());
int samples = Math.min(10, splits.length);
long recordsPerSample = sampleSize / samples;
int sampleStep = splits.length / samples;
long records = 0;
// take N samples from different parts of the input
for(int i=0; i < samples; ++i) {
RecordReader<Text,Text> reader =
inFormat.getRecordReader(splits[sampleStep * i], conf, null);
while (reader.next(key, value)) {
sampler.addKey(key);
records += 1;
if ((i+1) * recordsPerSample <= records) {
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)) {
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() {
return new Text();
}
public Text createValue() {
return new Text();
}
public long getPos() throws IOException {
return in.getPos();
}
public float getProgress() throws IOException {
return in.getProgress();
}
public boolean next(Text key, Text value) throws IOException {
if (in.next(junk, line)) {
if (line.getLength() < KEY_LENGTH) {
key.set(line);
value.clear();
} else {
byte[] bytes = line.getBytes();
key.set(bytes, 0, KEY_LENGTH);
value.set(bytes, KEY_LENGTH, line.getLength() - KEY_LENGTH);
}
return true;
} else {
return false;
}
}
}
@Override
public RecordReader<Text, Text>
getRecordReader(InputSplit split,
JobConf job,
Reporter reporter) throws IOException {
return new TeraRecordReader(job, (FileSplit) split);
}
@Override
public InputSplit[] getSplits(JobConf conf, int splits) throws IOException {
if (conf == lastConf) {
return lastResult;
}
lastConf = conf;
lastResult = super.getSplits(conf, splits);
return lastResult;
}
}