/**
* 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.mapred.lib;
import java.io.IOException;
import java.util.ArrayList;
import org.apache.hadoop.fs.FSDataInputStream;
import org.apache.hadoop.fs.FileStatus;
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.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.JobConfigurable;
import org.apache.hadoop.mapred.LineRecordReader;
import org.apache.hadoop.mapred.RecordReader;
import org.apache.hadoop.mapred.Reporter;
import org.apache.hadoop.util.LineReader;
/**
* NLineInputFormat which splits N lines of input as one split.
*
* In many "pleasantly" parallel applications, each process/mapper
* processes the same input file (s), but with computations are
* controlled by different parameters.(Referred to as "parameter sweeps").
* One way to achieve this, is to specify a set of parameters
* (one set per line) as input in a control file
* (which is the input path to the map-reduce application,
* where as the input dataset is specified
* via a config variable in JobConf.).
*
* The NLineInputFormat can be used in such applications, that splits
* the input file such that by default, one line is fed as
* a value to one map task, and key is the offset.
* i.e. (k,v) is (LongWritable, Text).
* The location hints will span the whole mapred cluster.
*/
public class NLineInputFormat extends FileInputFormat<LongWritable, Text>
implements JobConfigurable {
private int N = 1;
public RecordReader<LongWritable, Text> getRecordReader(
InputSplit genericSplit,
JobConf job,
Reporter reporter)
throws IOException {
reporter.setStatus(genericSplit.toString());
return new LineRecordReader(job, (FileSplit) genericSplit);
}
/**
* Logically splits the set of input files for the job, splits N lines
* of the input as one split.
*
* @see org.apache.hadoop.mapred.FileInputFormat#getSplits(JobConf, int)
*/
public InputSplit[] getSplits(JobConf job, int numSplits)
throws IOException {
ArrayList<FileSplit> splits = new ArrayList<FileSplit>();
for (FileStatus status : listStatus(job)) {
Path fileName = status.getPath();
if (status.isDir()) {
throw new IOException("Not a file: " + fileName);
}
FileSystem fs = fileName.getFileSystem(job);
LineReader lr = null;
try {
FSDataInputStream in = fs.open(fileName);
lr = new LineReader(in, job);
Text line = new Text();
int numLines = 0;
long begin = 0;
long length = 0;
int num = -1;
while ((num = lr.readLine(line)) > 0) {
numLines++;
length += num;
if (numLines == N) {
// NLineInputFormat uses LineRecordReader, which always reads (and
// consumes) at least one character out of its upper split
// boundary. So to make sure that each mapper gets N lines, we
// move back the upper split limits of each split by one character
// here.
if (begin == 0) {
splits.add(new FileSplit(fileName, begin, length - 1,
new String[] {}));
} else {
splits.add(new FileSplit(fileName, begin - 1, length,
new String[] {}));
}
begin += length;
length = 0;
numLines = 0;
}
}
if (numLines != 0) {
splits.add(new FileSplit(fileName, begin, length, new String[]{}));
}
} finally {
if (lr != null) {
lr.close();
}
}
}
return splits.toArray(new FileSplit[splits.size()]);
}
public void configure(JobConf conf) {
N = conf.getInt("mapred.line.input.format.linespermap", 1);
}
}