001/**
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements.  See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership.  The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License.  You may obtain a copy of the License at
009 *
010 *     http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing, software
013 * distributed under the License is distributed on an "AS IS" BASIS,
014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015 * See the License for the specific language governing permissions and
016 * limitations under the License.
017 */
018
019package org.apache.hadoop.mapred.lib;
020
021import java.io.IOException;
022import java.util.ArrayList;
023
024import org.apache.hadoop.classification.InterfaceAudience;
025import org.apache.hadoop.classification.InterfaceStability;
026import org.apache.hadoop.fs.FileStatus;
027import org.apache.hadoop.io.LongWritable;
028import org.apache.hadoop.io.Text;
029import org.apache.hadoop.mapred.FileInputFormat;
030import org.apache.hadoop.mapred.FileSplit;
031import org.apache.hadoop.mapred.InputSplit;
032import org.apache.hadoop.mapred.JobConf;
033import org.apache.hadoop.mapred.JobConfigurable;
034import org.apache.hadoop.mapred.LineRecordReader;
035import org.apache.hadoop.mapred.RecordReader;
036import org.apache.hadoop.mapred.Reporter;
037
038/**
039 * NLineInputFormat which splits N lines of input as one split.
040 *
041 * In many "pleasantly" parallel applications, each process/mapper 
042 * processes the same input file (s), but with computations are 
043 * controlled by different parameters.(Referred to as "parameter sweeps").
044 * One way to achieve this, is to specify a set of parameters 
045 * (one set per line) as input in a control file 
046 * (which is the input path to the map-reduce application,
047 * where as the input dataset is specified 
048 * via a config variable in JobConf.).
049 * 
050 * The NLineInputFormat can be used in such applications, that splits 
051 * the input file such that by default, one line is fed as
052 * a value to one map task, and key is the offset.
053 * i.e. (k,v) is (LongWritable, Text).
054 * The location hints will span the whole mapred cluster.
055 */
056@InterfaceAudience.Public
057@InterfaceStability.Stable
058public class NLineInputFormat extends FileInputFormat<LongWritable, Text> 
059                              implements JobConfigurable { 
060  private int N = 1;
061
062  public RecordReader<LongWritable, Text> getRecordReader(
063                                            InputSplit genericSplit,
064                                            JobConf job,
065                                            Reporter reporter) 
066  throws IOException {
067    reporter.setStatus(genericSplit.toString());
068    return new LineRecordReader(job, (FileSplit) genericSplit);
069  }
070
071  /** 
072   * Logically splits the set of input files for the job, splits N lines
073   * of the input as one split.
074   * 
075   * @see org.apache.hadoop.mapred.FileInputFormat#getSplits(JobConf, int)
076   */
077  public InputSplit[] getSplits(JobConf job, int numSplits)
078  throws IOException {
079    ArrayList<FileSplit> splits = new ArrayList<FileSplit>();
080    for (FileStatus status : listStatus(job)) {
081      for (org.apache.hadoop.mapreduce.lib.input.FileSplit split : 
082          org.apache.hadoop.mapreduce.lib.input.
083          NLineInputFormat.getSplitsForFile(status, job, N)) {
084        splits.add(new FileSplit(split));
085      }
086    }
087    return splits.toArray(new FileSplit[splits.size()]);
088  }
089
090  public void configure(JobConf conf) {
091    N = conf.getInt("mapreduce.input.lineinputformat.linespermap", 1);
092  }
093}