org.apache.hadoop.mapreduce.lib.input
Class NLineInputFormat

java.lang.Object
  org.apache.hadoop.mapreduce.InputFormat<K,V>
      org.apache.hadoop.mapreduce.lib.input.FileInputFormat<LongWritable,Text>
          org.apache.hadoop.mapreduce.lib.input.NLineInputFormat

@InterfaceAudience.Public
@InterfaceStability.Stable
public class NLineInputFormat
extends FileInputFormat<LongWritable,Text>

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.

Nested Class Summary

Nested classes/interfaces inherited from class org.apache.hadoop.mapreduce.lib.input.FileInputFormat

FileInputFormat.Counter

Field Summary

static String

LINES_PER_MAP

Constructor Summary

NLineInputFormat()

Method Summary

protected static FileSplit	createFileSplit(Path fileName, long begin, long length) NLineInputFormat uses LineRecordReader, which always reads (and consumes) at least one character out of its upper split boundary.
RecordReader<LongWritable,Text>	createRecordReader(InputSplit genericSplit, TaskAttemptContext context) Create a record reader for a given split.
static int	getNumLinesPerSplit(JobContext job) Get the number of lines per split
List<InputSplit>	getSplits(JobContext job) Logically splits the set of input files for the job, splits N lines of the input as one split.
static List<FileSplit>	getSplitsForFile(FileStatus status, Configuration conf, int numLinesPerSplit)
static void	setNumLinesPerSplit(Job job, int numLines) Set the number of lines per split

Methods inherited from class org.apache.hadoop.mapreduce.lib.input.FileInputFormat

addInputPath, addInputPaths, computeSplitSize, getBlockIndex, getFormatMinSplitSize, getInputPathFilter, getInputPaths, getMaxSplitSize, getMinSplitSize, isSplitable, listStatus, setInputPathFilter, setInputPaths, setInputPaths, setMaxInputSplitSize, setMinInputSplitSize

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

LINES_PER_MAP

public static final String LINES_PER_MAP

See Also:

Constant Field Values

Constructor Detail

NLineInputFormat

public NLineInputFormat()

Method Detail

createRecordReader

public RecordReader<LongWritable,Text> createRecordReader(InputSplit genericSplit,
                                                          TaskAttemptContext context)
                                                   throws IOException

Description copied from class: InputFormat

Create a record reader for a given split. The framework will call RecordReader.initialize(InputSplit, TaskAttemptContext) before the split is used.

Specified by:

createRecordReader in class InputFormat<LongWritable,Text>

Parameters:

genericSplit - the split to be read

context - the information about the task

Returns:

a new record reader

Throws:

IOException

getSplits

public List<InputSplit> getSplits(JobContext job)
                           throws IOException

Logically splits the set of input files for the job, splits N lines of the input as one split.

Overrides:

getSplits in class FileInputFormat<LongWritable,Text>

Parameters:

job - job configuration.

Returns:

an array of InputSplits for the job.

Throws:

IOException

See Also:

FileInputFormat.getSplits(JobContext)

getSplitsForFile

public static List<FileSplit> getSplitsForFile(FileStatus status,
                                               Configuration conf,
                                               int numLinesPerSplit)
                                        throws IOException

Throws:

IOException

createFileSplit

protected static FileSplit createFileSplit(Path fileName,
                                           long begin,
                                           long length)

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.

Parameters:

fileName - Path of file

begin - the position of the first byte in the file to process

length - number of bytes in InputSplit

Returns:

FileSplit

setNumLinesPerSplit

public static void setNumLinesPerSplit(Job job,
                                       int numLines)

Set the number of lines per split

Parameters:

job - the job to modify

numLines - the number of lines per split

getNumLinesPerSplit

public static int getNumLinesPerSplit(JobContext job)

Get the number of lines per split

Parameters:

job - the job

Returns:

the number of lines per split