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
019 package org.apache.hadoop.mapred.lib;
020
021 import java.io.IOException;
022 import java.util.ArrayList;
023
024 import org.apache.hadoop.classification.InterfaceAudience;
025 import org.apache.hadoop.classification.InterfaceStability;
026 import org.apache.hadoop.fs.FileStatus;
027 import org.apache.hadoop.fs.Path;
028 import org.apache.hadoop.io.LongWritable;
029 import org.apache.hadoop.io.Text;
030 import org.apache.hadoop.mapred.FileInputFormat;
031 import org.apache.hadoop.mapred.FileSplit;
032 import org.apache.hadoop.mapred.InputSplit;
033 import org.apache.hadoop.mapred.JobConf;
034 import org.apache.hadoop.mapred.JobConfigurable;
035 import org.apache.hadoop.mapred.LineRecordReader;
036 import org.apache.hadoop.mapred.RecordReader;
037 import 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
059 public 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 }