/**
* 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.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
import org.apache.hadoop.fs.FileStatus;
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;
/**
* 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.
*/
@InterfaceAudience.Public
@InterfaceStability.Stable
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)) {
for (org.apache.hadoop.mapreduce.lib.input.FileSplit split :
org.apache.hadoop.mapreduce.lib.input.
NLineInputFormat.getSplitsForFile(status, job, N)) {
splits.add(new FileSplit(split));
}
}
return splits.toArray(new FileSplit[splits.size()]);
}
public void configure(JobConf conf) {
N = conf.getInt("mapreduce.input.lineinputformat.linespermap", 1);
}
}