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.fs.Path; 028import org.apache.hadoop.io.LongWritable; 029import org.apache.hadoop.io.Text; 030import org.apache.hadoop.mapred.FileInputFormat; 031import org.apache.hadoop.mapred.FileSplit; 032import org.apache.hadoop.mapred.InputSplit; 033import org.apache.hadoop.mapred.JobConf; 034import org.apache.hadoop.mapred.JobConfigurable; 035import org.apache.hadoop.mapred.LineRecordReader; 036import org.apache.hadoop.mapred.RecordReader; 037import org.apache.hadoop.mapred.Reporter; 038 039/** 040 * NLineInputFormat which splits N lines of input as one split. 041 * 042 * In many "pleasantly" parallel applications, each process/mapper 043 * processes the same input file (s), but with computations are 044 * controlled by different parameters.(Referred to as "parameter sweeps"). 045 * One way to achieve this, is to specify a set of parameters 046 * (one set per line) as input in a control file 047 * (which is the input path to the map-reduce application, 048 * where as the input dataset is specified 049 * via a config variable in JobConf.). 050 * 051 * The NLineInputFormat can be used in such applications, that splits 052 * the input file such that by default, one line is fed as 053 * a value to one map task, and key is the offset. 054 * i.e. (k,v) is (LongWritable, Text). 055 * The location hints will span the whole mapred cluster. 056 */ 057@InterfaceAudience.Public 058@InterfaceStability.Stable 059public class NLineInputFormat extends FileInputFormat<LongWritable, Text> 060 implements JobConfigurable { 061 private int N = 1; 062 063 public RecordReader<LongWritable, Text> getRecordReader( 064 InputSplit genericSplit, 065 JobConf job, 066 Reporter reporter) 067 throws IOException { 068 reporter.setStatus(genericSplit.toString()); 069 return new LineRecordReader(job, (FileSplit) genericSplit); 070 } 071 072 /** 073 * Logically splits the set of input files for the job, splits N lines 074 * of the input as one split. 075 * 076 * @see org.apache.hadoop.mapred.FileInputFormat#getSplits(JobConf, int) 077 */ 078 public InputSplit[] getSplits(JobConf job, int numSplits) 079 throws IOException { 080 ArrayList<FileSplit> splits = new ArrayList<FileSplit>(); 081 for (FileStatus status : listStatus(job)) { 082 for (org.apache.hadoop.mapreduce.lib.input.FileSplit split : 083 org.apache.hadoop.mapreduce.lib.input. 084 NLineInputFormat.getSplitsForFile(status, job, N)) { 085 splits.add(new FileSplit(split)); 086 } 087 } 088 return splits.toArray(new FileSplit[splits.size()]); 089 } 090 091 public void configure(JobConf conf) { 092 N = conf.getInt("mapreduce.input.lineinputformat.linespermap", 1); 093 } 094 095 /** 096 * NLineInputFormat uses LineRecordReader, which always reads 097 * (and consumes) at least one character out of its upper split 098 * boundary. So to make sure that each mapper gets N lines, we 099 * move back the upper split limits of each split 100 * by one character here. 101 * @param fileName Path of file 102 * @param begin the position of the first byte in the file to process 103 * @param length number of bytes in InputSplit 104 * @return FileSplit 105 */ 106 protected static FileSplit createFileSplit(Path fileName, long begin, long length) { 107 return (begin == 0) 108 ? new FileSplit(fileName, begin, length - 1, new String[] {}) 109 : new FileSplit(fileName, begin - 1, length, new String[] {}); 110 } 111}